docs: added usage documentation to readme (#3)

README.md

@@ -5,6 +5,70 @@
 
 The git provider for [go-semantic-release](https://github.com/go-semantic-release/semantic-release).
 
+This plugin will make sure that the continuous integration environment
+conditions are met. Namely that the release is happening on the
+correct branch.
+
+## Usage
+
+To use this plugin you need to include the following block in your
+`.semrelrc` file.
+
+```json
+{
+    "plugins": {
+        "provider": {
+            "name": "git",
+            // Options can be omitted if you want to use the defaults.
+            // See the section on configuration below.
+            "options": {
+                // Put configuration options here
+            }
+        }
+    }
+}
+```
+
+### Configuration
+
+|       Name       |        Default Value        |                    Description                     |
+|:----------------:|:---------------------------:|:--------------------------------------------------:|
+| default_branch   | master                      | The branch where deployments should happen.        |
+| tagger_name      | semantic-release            | The name of the user creating the tag.             |
+| tagger_email     | git@go-semantic-release.xyz | The email address of the user creating the tag.    |
+| remote_name      |                             | The name of the remote to push to.                 |
+| auth             | *(Depends on origin URL)*   | The authentication type to use (basic, ssh)        |
+| auth_username    | git                         | The name of the user to use for authentication.    |
+| auth_password    |                             | The password to use for basic auth or the SSH key. |
+| auth_private_key |                             | The path to an SSH private key file.               |
+| git_path         | .                           | The path to the Git repository                     |
+
+### Authentication
+
+#### Automatic
+
+If you don't pick a specific authentication mechanism then an
+authentication mechanism will be picked based on the URL of the Git
+remote. Under the covers [go-git](https://pkg.go.dev/github.com/go-git/go-git)
+is responsible for determining how to perform this kind of
+authentication.
+
+#### Basic
+
+Basic authentication uses a username and password pair to perform
+authentication over HTTP/HTTPS.
+
+For this method you'll need to set `auth_username` and `auth_password`.
+
+#### SSH
+
+SSH authentication uses an SSH private key to authenticate with the
+Git remote ove ran SSH connection.
+
+For this method you'll need to set `auth_username` and
+`auth_private_key`. If your private key uses a password then you'll
+also need to set `auth_password`.
+
 ## Licence
 
 The [MIT License (MIT)](http://opensource.org/licenses/MIT)