Updated README

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:git
+FROM alpine/git
 
 LABEL "repository"="http://github.com/UnicornGlobal/has-changes-action"
 LABEL "homepage"="http://github.com/UnicornGlobal/has-changes-action"

README.md

@@ -1,5 +1,47 @@
-# GitHub action for checking if a repo has uncommitted changes
+# Has Changes
 
-This is useful for things like checking if you need to open a
-pull request for changes that may be introduced through another
-action.
+GitHub action for checking if the repo is dirty (has uncommitted changes).
+
+## Why?
+
+This is useful for things like checking if you need to open a pull
+request for any changes that may be introduced through another action.
+
+## How?
+
+Add a step in a job after any steps whose code changes you want to check.
+
+You will then be able to check the status in subsequent steps.
+
+You do this by checking if `changed` is equal to `1`.
+
+The value will be 0 if no code has been changed by any previous steps.
+
+## Example
+
+```yaml
+name: Has Changes
+jobs:
+  has-changes:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        ref: ${{ github.head_ref }}
+    - name: Make changes
+      run: touch change.temp
+    # This step will evaluate the repo status and report the change
+    - name: Check if there are changes
+      id: changes
+      uses: UnicornGlobal/[email protected]
+    # You can now access a variable indicating if there have been changes
+    - name: Process changes
+      if: steps.changes.outputs.changed == 1
+      run: echo "Changes exist"
+```
+
+The example shows that adding a step to check the status will expose the
+status on the `${{ steps.changes.outputs.changed }}` variable.
+
+The `steps.changes` is defined by the `id: changes`. If you change the id
+value then the step name must change too (as it references the id).