doc: fixes in image-handling.md

Signed-off-by: Alberto Donato <alberto.donato@canonical.com>

doc/image-handling.md

@@ -13,18 +13,18 @@ When spawning a container from a remote image, the remote image is
 downloaded into the local image store with the cached bit set. The image
 will be kept locally as a private image until either it's been unused
 (no new container spawned) for the number of days set in
-images.remote\_cache\_expiry or until the image's expiry is reached
+`images.remote_cache_expiry` or until the image's expiry is reached
 whichever comes first.
 
-LXD keeps track of image usage by updating the last\_used\_at image
+LXD keeps track of image usage by updating the `last_used_at` image
 property every time a new container is spawned from the image.
 
 # Auto-update
 LXD can keep images up to date. By default, any image which comes from a
 remote server and was requested through an alias will be automatically
-updated by LXD. This can be changed with images.auto\_update\_cached.
+updated by LXD. This can be changed with `images.auto_update_cached`.
 
-On startup and then every 6 hours (unless images.auto\_update\_interval
+On startup and then every 6 hours (unless `images.auto_update_interval`
 is set), the LXD daemon will go look for more recent version of all the
 images in the store which are marked as auto-update and have a recorded
 source server.
@@ -43,7 +43,7 @@ created from it, LXD will use the previous version of the image rather
 than delay the container creation.
 
 This behavior only happens if the current image is scheduled to be
-auto-updated and can be disabled by setting images.auto\_update\_interval to 0.
+auto-updated and can be disabled by setting `images.auto_update_interval` to 0.
 
 # Image format
 LXD currently supports two LXD-specific image formats.
@@ -62,20 +62,22 @@ non-LXD rootfs tarballs already available today.
 
 ## Unified tarball
 Tarball, can be compressed and contains:
- - rootfs/
- - metadata.yaml
- - templates/ (optional)
+
+ - `rootfs/`
+ - `metadata.yaml`
+ - `templates/` (optional)
 
 In this mode, the image identifier is the SHA-256 of the tarball.
 
 ## Split tarballs
 Two (possibly compressed) tarballs. One for metadata, one for the rootfs.
 
-metadata.tar contains:
- - metadata.yaml
- - templates/ (optional)
+`metadata.tar` contains:
+
+ - `metadata.yaml`
+ - `templates/` (optional)
 
-rootfs.tar contains a Linux root filesystem at its root.
+`rootfs.tar` contains a Linux root filesystem at its root.
 
 In this mode the image identifier is the SHA-256 of the concatenation of
 the metadata and rootfs tarball (in that order).
@@ -85,62 +87,67 @@ The tarball(s) can be compressed using bz2, gz, xz, lzma, tar (uncompressed) or
 it can also be a squashfs image.
 
 ## Content
-The rootfs directory (or tarball) contains a full file system tree of what will become the container's /.
+The rootfs directory (or tarball) contains a full file system tree of what will become the container's `/`.
 
 The templates directory contains pongo2-formatted templates of files inside the container.
 
-metadata.yaml contains information relevant to running the image under
+`metadata.yaml` contains information relevant to running the image under
 LXD, at the moment, this contains:
 
-    architecture: x86_64
-    creation_date: 1424284563
+```yaml
+architecture: x86_64
+creation_date: 1424284563
+properties:
+  description: Ubuntu 14.04 LTS Intel 64bit
+  os: Ubuntu
+  release:
+    - trusty
+    - 14.04
+templates:
+  /etc/hosts:
+    when:
+      - create
+      - rename
+    template: hosts.tpl
     properties:
-      description: Ubuntu 14.04 LTS Intel 64bit
-      os: Ubuntu
-      release:
-        - trusty
-        - 14.04
-    templates:
-      /etc/hosts:
-        when:
-          - create
-          - rename
-        template: hosts.tpl
-        properties:
-          foo: bar
-      /etc/hostname:
-        when:
-          - start
-        template: hostname.tpl
-      /etc/network/interfaces:
-        when:
-          - create
-        template: interfaces.tpl
-        create_only: true
-
-The architecture and creation\_date fields are mandatory, the properties
+      foo: bar
+  /etc/hostname:
+    when:
+      - start
+    template: hostname.tpl
+  /etc/network/interfaces:
+    when:
+      - create
+    template: interfaces.tpl
+    create_only: true
+```
+
+The `architecture` and `creation_date` fields are mandatory, the properties
 are just a set of default properties for the image. The os, release,
 name and description fields while not mandatory in any way, should be
 pretty common.
 
-For templates, the "when" key can be one or more of:
- - create (run at the time a new container is created from the image)
- - copy (run when a container is created from an existing one)
- - start (run every time the container is started)
+For templates, the `when` key can be one or more of:
+
+ - `create` (run at the time a new container is created from the image)
+ - `copy` (run when a container is created from an existing one)
+ - `start` (run every time the container is started)
 
 The templates will always receive the following context:
- - trigger: name of the event which triggered the template (string)
- - path: path of the file being templated (string)
- - container: key/value map of container properties (name, architecture, privileged and ephemeral) (map[string]string)
- - config: key/value map of the container's configuration (map[string]string)
- - devices: key/value map of the devices assigned to this container (map[string]map[string]string)
- - properties: key/value map of the template properties specified in metadata.yaml (map[string]string)
 
-The "create\_only" key can be set to have LXD only only create missing files but not overwrite an existing file.
+ - `trigger`: name of the event which triggered the template (string)
+ - `path`: path of the file being templated (string)
+ - `container`: key/value map of container properties (name, architecture, privileged and ephemeral) (map[string]string)
+ - `config`: key/value map of the container's configuration (map[string]string)
+ - `devices`: key/value map of the devices assigned to this container (map[string]map[string]string)
+ - `properties`: key/value map of the template properties specified in metadata.yaml (map[string]string)
+
+The `create_only` key can be set to have LXD only only create missing files but not overwrite an existing file.
 
 As a general rule, you should never template a file which is owned by a
 package or is otherwise expected to be overwritten by normal operation
 of the container.
 
 For convenience the following functions are exported to pongo templates:
- - config\_get("user.foo", "bar") => Returns the value of "user.foo" or "bar" if unset.
+
+ - `config_get("user.foo", "bar")` => Returns the value of `user.foo` or `"bar"` if unset.