Update github readme with org:team syntax

docs/source/github.md

@@ -39,3 +39,33 @@ To use this expanded user information, you will need to subclass your
 current spawner and modify the subclass to read these fields from
 `auth_state` and then use this information to provision your Notebook or
 Lab user.
+
+## Restricting access
+
+### Organizations
+
+If you would like to restrict access to members of specific GitHub organizations
+you can pass a list of organization names to `allowed_organizations`.
+
+For example, the below will ensure that only members of `org_a` or
+`org_b` will be authorized to access.
+
+`c.GitHubOAuthenticator.allowed_organizations = ["org_a", "org_b"]`
+
+### Teams
+
+It is also possible to restrict access to members of specific teams within
+organizations using the syntax: `<organization>:<team-name>`.
+
+For example, the below will only allow members of `org_a`, or
+`team_1` in `org_b` access. Members of `org_b` but not `team_1` will be
+unauthorized to access.
+
+`c.GitHubOAuthenticator.allowed_organizations = ["org_a", "org_b:team_1"]`
+
+### Notes
+
+- Restricting access by either organization or team requires the `read:org`
+  scope
+- Ensure you use the organization/team name as it appears in the GitHub url
+  - E.g. Use `jupyter` instead of `Project Jupyter`