docs: add features, setup and usage instructions to readme

README.md

@@ -1,3 +1,25 @@
 # nixpkgs-review-gha
 
 Run [nixpkgs-review](https://github.com/Mic92/nixpkgs-review) in GitHub Actions
+
+## Features
+- Build on `x86_64-linux`, `aarch64-linux`, `x86_64-darwin` and `aarch64-darwin`
+- No local setup
+- Automatically post results on the reviewed pull request
+- Wait for [upstream evaluation](https://github.com/NixOS/nixpkgs/blob/master/.github/workflows/eval.yml) to finish before running nixpkgs-review
+- Optionally start a [tmate](https://tmate.io/) session after nixpkgs-review has finished to allow interactive testing/debugging via SSH
+
+## Setup
+1. [Fork](https://github.com/Defelo/nixpkgs-review-gha/fork) this repository.
+2. In your fork, go to the [Actions](../../actions) tab and enable GitHub Actions workflows.
+3. (optional) If you want nixpkgs-review-gha to automatically post the results on the reviewed pull requests, you need to generate a [personal access token](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/managing-your-personal-access-tokens):
+    1. Go to <https://github.com/settings/tokens> and generate a new **classic** token with the `public_repo` scope.
+    2. In your fork, go to "Settings" > "Secrets and variables" > "actions" and [add a new repository secret](../../settings/secrets/actions/new):
+        - name: `GH_TOKEN`
+        - value: the personal access token you generated before
+
+## Usage
+1. Open the [review workflow in the "Actions" tab](../../actions/workflows/review.yml)
+2. Click on "Run workflow"
+3. Enter the number of the pull request in nixpkgs you would like to review and click on "Run workflow"
+4. Reload the page if necessary and click on the review run to see the logs