Add basic info to README

Author: krzema12

README.md

@@ -1,2 +1,61 @@
-# github-actions-typing
+# Work in progress! Not ready for usage.
+
+---
+
+# GitHub Actions typing
+
 Bring type-safety to your GitHub actions' API!
+
+This is a GitHub action that validates your action's manifest (action.y(a)ml) and ensures the inputs and outputs have
+types set according to a certain specification.
+
+# Example
+
+Let's say your action has such manifest:
+
+```yaml
+name: My cool action
+description: Just to showcase GitHub Actions typing
+typingSpec: krzema12/[email protected]
+inputs:
+  verbose:
+    description: 'Set to true to display debug information helpful when troubleshooting issues with this action.'
+    required: false
+    default: 'false'
+    type: boolean
+  log-level:
+    description: 'Specify the level of details for logging.'
+    required: true
+  permissions:
+    description: 'Who should have access.'
+    type: inttteger
+runs:
+  using: 'node16'
+  image: 'dist/main.js'
+```
+
+This action, once used within a workflow, will fail the workflow run and produce such output:
+
+![Example output](docs/ExampleOutput.png)
+
+# Usage
+
+Create a workflow in your actions' repository that will simply call this action:
+
+```yaml
+name: Validate action typings
+
+on:
+    push: [main]
+    pull_request:
+    workflow_dispatch:
+
+jobs:
+    validate-typings:
+        runs-on: "ubuntu-latest"
+        steps:
+        - uses: actions/checkout@v3
+        - uses: krzema12/github-actions-typing@v0
+          with:
+            verbose: true
+```