Update readme

README.md

@@ -1,19 +1,28 @@
-#vcpkg-action
+# vcpkg-action
 
-`vcpkg-action` is a simple action to build and cache vcpkg packages. It currently only supports Windows. `vcpkg` is cloned in the `${{ github.workspace }}\vcpkg` directory, and the build products are located in `${{ github.workspace }}\vcpkg\installed\<triplet>`. For cmake, use the option:
+`vcpkg-action` is a simple action to build and cache vcpkg packages. It supports all platforms. It has two unique
+features:
+
+* Simplicity
+* Use of a "dry-run" build to generate a unique cache key for the configuration. This guarantees that if packages
+  change, the cache will be rebuilt, but avoids rebuilding when it isn't necessary.
+
+`vcpkg` is cloned to the `${{ github.workspace }}\vcpkg` directory, and the build products are located in
+ `${{ github.workspace }}\vcpkg\installed\<triplet>`. For cmake, use the option:
 
 ```
- -DCMAKE_TOOLCHAIN_FILE=${{ github.workspace }}/vcpkg/scripts/buildsystems/vcpkg.cmake
-        -DVCPKG_TARGET_TRIPLET=<triplet>
+ -DCMAKE_TOOLCHAIN_FILE=${{ github.workspace }}/vcpkg/scripts/buildsystems/vcpkg.cmake -DVCPKG_TARGET_TRIPLET=<triplet>
 ```
 
-Another directory named `vcpkg_cache` is created in the workspace root. This directory is used to store the cache files, and is cached using `pat-s/always-upload-cache@v3`. The cache key is automatically generated, but can also be modified using the `cache-key` argument.
+Another directory named `vcpkg_cache` is created in the workspace root. This directory is used to store the cache files, 
+and is cached using `pat-s/always-upload-cache@v3`. The cache key is automatically generated, 
+but can also be modified using the `cache-key` argument.
 
-Example usage:
+Simple usage example:
 
 ```yaml
 - name: vcpkg build
-  uses: johnwason/vcpkg-action@v1
+  uses: johnwason/vcpkg-action@v2
   with:
     pkgs: boost-date-time boost-system
     triplet: x64-windows-release
@@ -22,7 +31,7 @@ Example usage:
 ## Usage
 
 ```yaml
-- uses: johnwason/vcpkg-action@v1
+- uses: johnwason/vcpkg-action@v2
   with:
     # The vcpkg packages to build, separated by spaces
     pkgs: ''
@@ -31,7 +40,36 @@ Example usage:
     triplet: ''
     # Extra arguments to pass to vcpkg command (optional)
     extra-args: ''
-    # Additional string to add to cache key (optional)
+    # Additional string to add to cache key. If using a build matrix or building different configurations
+    # on the same operating system, be sure to include an additional cache key to separate the caches. (optional)
     cache-key: ''
 
 ```
+
+## Advanced Example
+
+The following is an advanced example with a matrix build. Note that the runner name is included as an additional
+cache key.
+
+```yaml
+jobs:
+  buildme:
+    runs-on: ${{ matrix.config.os }}
+    strategy:
+      matrix:
+        config:
+        - os: ubuntu-20.04
+          vcpkg_triplet: x64-linux-release
+        - os: macos-11
+          vcpkg_triplet: x64-osx-release
+        - os: windows-2019
+          vcpkg_triplet: x64-windows-release
+    steps:
+      - name: vcpkg build
+        uses: johnwason/vcpkg-action@v2
+        with:
+          pkgs: boost-date-time
+          triplet: ${{ matrix.config.vcpkg_triplet }}
+          cache-key: ${{ matrix.config.os }}
+```
+