Updated example of profile updating and saving (#372)

It was discovered that using profile.config and profile.devices as left-hand-sides to a .update function was setting them to "none" and the profile.update() was not actually saving.  profile.save() was also causing the profile settings to be blanked out due to the NoneTypes being set to profile.config and profile.devices.  Also expanded profile attribute descriptions to explicitly note types

doc/source/profiles.rst

@@ -21,11 +21,11 @@ methods:
 Profile attributes
 ------------------
 
-  - `config` - config options for containers
-  - `description` - The description of the profile
-  - `devices` - device options for containers
-  - `name` - The name of the profile
-  - `used_by` - A list of containers using this profile
+  - `config` - (dict) config options for containers
+  - `description` - (str) The description of the profile
+  - `devices` - (dict) device options for containers
+  - `name` - (str) name of the profile
+  - `used_by` - (list) containers using this profile
 
 
 Profile methods
@@ -51,8 +51,9 @@ Containers and Images. Profiles are keyed on a unique name.
 
 The profile can then be modified and saved.
 
-    >>> profile.config = profile.config.update({'security.nesting': 'true'})
-    >>> profile.update()
+    >>> profile.config.update({'security.nesting': 'true'})
+    >>> profile.devices.update({"eth0": {"parent": "lxdbr0", "nictype": "bridged", "type": "nic", "name": "eth0"}})
+    >>> profile.save()
 
 
 To create a new profile, use `create` with a name, and optional `config`