Update README.md

Author: Danny McCormick

README.md

@@ -1,10 +1,38 @@
-# @actions/setup-dotnet
+# setup-dotnet
 
-This action sets by Dotnet environment for use in actions by:
+This action sets up a dotnet environment for use in actions by:
 
-- optionally downloading and caching a version of Dotnet
-- registering problem matchers for error output 
-- TODO: configuring proxy if the runner is configured to use a proxy (coming with private runners)
+- optionally downloading and caching a version of dotnet by version and adding to PATH
+- registering problem matchers for error output
+
+# Usage
+
+See [action.yml](action.yml)
+
+Basic:
+```yaml
+actions:
+- uses: actions/setup-dotnet@latest
+  with:
+    version: 2.2.103 // Version to use.
+- run: dotnet build <my project>
+```
+
+Matrix Testing:
+```yaml
+jobs:
+  build:
+    strategy:
+      matrix:
+        dotnet: [ 2.2.103, 3.5.2, 4.5.1 ]
+    name: Dotnet ${{ matrix.dotnet }} sample
+    actions:
+      - name: Setup dotnet
+        uses: actions/setup-dotnet@latest
+        with:
+          version: ${{ matrix.dotnet }}
+      - run: dotnet build <my project>
+```
 
 # License