*: document the GitHub connector

Documentation/github-connector.md

@@ -0,0 +1,32 @@
+# Authentication through GitHub
+
+## Overview
+
+One of the login options for dex uses the GitHub OAuth2 flow to identify the end user through their GitHub account.
+
+When a client redeems a refresh token through dex, dex will re-query GitHub to update user information in the ID Token. To do this, __dex stores a readonly GitHub access token in its backing datastore.__ Users that reject dex's access through GitHub will also revoke all dex clients which authenticated them through GitHub.
+
+## Configuration
+
+Register a new application with [GitHub][github-oauth2] ensuring the callback URL is `(dex issuer)/callback`. For example if dex is listening at the non-root path `https://auth.example.com/dex` the callback would be `https://auth.example.com/dex/callback`.
+
+The following is an example of a configuration for `examples/config-dev.yaml`:
+
+```yaml
+connectors:
+- type: github
+  id: github
+  name: GitHub
+  config:
+    # Credentials can be string literals or pulled from the environment.
+    clientID: $GITHUB_CLIENT_ID
+    clientSecret: $GITHUB_CLIENT_SECRET
+    redirectURI: http://127.0.0.1:5556/dex/callback
+    # Optional organization to pull teams from, communicate through the
+    # "groups" scope.
+    #
+    # NOTE: This is an EXPERIMENTAL config option and will likely change.
+    org: my-oranization
+```
+
+[github-oauth2]: https://github.com/settings/applications/new

README.md

@@ -27,6 +27,7 @@ Standards-based token responses allows applications to interact with any OpenID
 * [gRPC API](Documentation/api.md)
 * Identity provider logins
   * [LDAP](Documentation/ldap-connector.md)
+  * [GitHub](Documentation/github-connector.md)
 * Client libraries
   * [Go][go-oidc]