added usage example to the README

Author: gtaschuk

README.md

@@ -1,3 +1,35 @@
 # graph-deploy
 
-Graph Deploy is a github action that deploys a subgraph to the graph protocol to index Ethereum and IPFS as a graphql
+GitHub action that deploys a subgraph to the graph protocol to index Ethereum and IPFS as graphql
+
+Set your thegraph.com access token as a github secret in your repository, and add `.github/workflows/graph.yml`:
+
+```yml
+name: Deploy Graph
+
+on:
+  push:
+    branches: main
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install node
+        uses: actions/setup-node@v1
+        with:
+          node-version: 14
+      - name: Install
+        run: yarn --frozen-lockfile
+      - name: Codegen
+        run: yarn codegen
+      - name: Build
+        run: yarn build
+      - uses: gtaschuk/graph-deploy@v0.1.0
+        with:
+          graph_access_token: ${{secrets.GRAPH_ACCESS_TOKEN}}
+          graph_subgraph_name: "your-subgraph-name"
+          graph_account: "your-github-name-or-organization"
+          graph_config_file: "subgraph.yml"
+```