Add docs

Author: cgay

README.md

@@ -1,2 +1,37 @@
 # install-opendylan
-GitHub Action to install Open Dylan
+
+A GitHub Action to install the Open Dylan compiler.
+
+Example:
+
+```yaml
+    - uses: dylan-lang/install-opendylan@v1
+      with:
+        version: 2020.1
+```
+
+The version is optional and will generally default to the latest release.
+
+Complete job example using the `strings` library:
+
+```yaml
+jobs:
+  build-and-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dylan-lang/install-opendylan@v1
+
+      - name: Build strings-test-suite
+        run: ./dylan-compiler -build -jobs 3 strings-test-suite
+
+      - name: Run strings-test-suite
+        run: _build/bin/strings-test-suite
+```
+
+When this Action has completed two artifacts exist at the top-level in your
+GitHub workspace:
+
+1.  A symbolic link named `opendylan` that points to the Open Dylan
+    installation directory.
+
+2.  A link to the `dylan-compiler` binary.