update configuration doc

.gitignore

@@ -1 +1,2 @@
 git-mirror
+config.yaml

readme.md

@@ -1,11 +1,89 @@
-git-mirror is a golang library to periodically mirror (bare clones) remote repositories locally.
-The mirror is created with `--mirror=fetch` hence everything in `refs/*` on the remote
-will be directly mirrored into `refs/*` in the local repository. 
-it can also maintain multiple mirrored checked out worktrees on different references.
+# git-mirror
+
+git-mirror is an app to periodically mirror (bare clones) remote repositories locally.
+It supports multiple mirrored checked out worktrees on different references
+and it can also mirror multiple repositories.
 
+`git-mirror` can be used as golang library in your code. [docs](https://pkg.go.dev/github.com/utilitywarehouse/git-mirror/pkg/mirror)  
+The mirror is created with `--mirror=fetch` hence everything in `refs/*` on the remote
+will be directly mirrored into `refs/*` in the local repository.
 
 The implementation borrows heavily from [kubernetes/git-sync](https://github.com/kubernetes/git-sync).
 If you want to sync single repository on one reference then you are probably better off
 with [kubernetes/git-sync](https://github.com/kubernetes/git-sync), as it provides
 a lot more customisation. 
 `git-mirror` should be used if multiple mirrored repositories with multiple checked out branches (worktrees) is required.
+
+## Usage
+
+```
+Usage:
+    git-mirror [global options]
+
+GLOBAL OPTIONS:
+    -log-level value    (default: 'info') Log level [$LOG_LEVEL]
+    -config value       (default: '/etc/git-mirror/config.yaml') Absolute path to the config file. [$GIT_MIRROR_CONFIG]
+    -watch-config value (default: true) watch config for changes and reload when changes encountered. [$GIT_MIRROR_WATCH_CONFIG]
+```
+
+## Config
+configuration file contains `default` parameters and list of repositories.
+each repository also contains list of worktrees to checkout.
+`defaults` fields values are used if repository parameters are not specified.
+
+```yaml
+defaults:
+  # root is the absolute path to the root dir where all repositories directories
+  # will be created all repos worktree links will be created here if not
+  # specified in repo config (default: '/tmp/git-mirror')
+  root: /tmp/git-mirror
+
+  # interval is time duration for how long to wait between mirrors. (default: '30s')
+  interval: 30s
+
+  # mirrorTimeout represents the total time allowed for the complete mirror loop (default: '2m')
+  mirror_timeout: 2m
+
+  # git_gc garbage collection string. valid values are
+  # 'auto', 'always', 'aggressive' or 'off' (default: 'always')
+  git_gc: always
+
+  # auth config to fetch remote repos
+  auth:
+    # path to the ssh key & known hosts used to fetch remote
+    ssh_key_path: /etc/git-secret/ssh
+    ssh_known_hosts_path: /etc/git-secret/known_hosts
+repositories:
+  - remote: https://github.com/utilitywarehouse/git-mirror # required
+    # remote is the git URL of the remote repository to mirror.
+    # supported urls are 'git@host.xz:org/repo.git','ssh://git@host.xz/org/repo.git'
+    # or 'https://host.xz/org/repo.git'. '.git' suffix is optional
+
+    # following fields are optional.
+    # if these fields are not specified values from defaults section will be used
+    root: /some/other/location
+    interval: 1m
+    mirror_timeout: 5m
+    git_gc: always
+    auth:
+      ssh_key_path: /some/other/location
+      ssh_known_hosts_path: /some/other/location
+    worktrees:
+      - link: alerts # required
+        # link is the path at which to create a symlink to the worktree dir
+        # if path is not absolute it will be created under repository root
+
+        ref: main
+        # ref represents the git reference of the worktree branch, tags or hash
+        # are supported. default is HEAD
+
+        pathspec: example
+        # pathspec of the dirs to checkout if required, optional if omitted
+        # whole repo will be checked out
+```
+
+App can load changes in config without restart. At repository level only 
+adding and removing repository is supported. changes in interval, timeout 
+and auth will require an app restart. 
+At worktree level apart from adding or removing, changes in existing worktree's
+link, ref and pathspec is supported.