Update action to reflect reality

This was from an earlier design choice, and I just forgot to remove
some remaining traces of the old `gh-pages` stuff.

Author: dead-claudia

README.md

@@ -31,7 +31,7 @@ It's a multi-step process.
      ```yml
      - uses: MithrilJS/infra/deploy@main
        with:
-         type: gh-pages
+         type: github-pages
          token: ${{ secrets.DEPLOY_TOKEN }}
      ```
    To deploy a package not located in the repo root, set the `root_dir` option:

deploy/action.yml

@@ -2,7 +2,10 @@ name: Request a deployment
 
 inputs:
   type:
-    description: The type of deployment to perform.
+    description: |
+      The type of deployment to perform. Currently must be one of the following:
+      - `npm`
+      - `github-pages`
     required: true
   root_dir:
     description: The directory to the root. Defaults to `GITHUB_WORKSPACE`.