Added a cache example when using matrix

examples.md

@@ -345,6 +345,31 @@ Replace `~/.cache/pip` with the correct `path` if not using Ubuntu.
       ${{ runner.os }}-pip-
 ```
 
+### Multiple OS's in a workflow with a matrix
+
+``` yaml
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        include:
+        - os: ubuntu-latest
+          path: ~/.cache/pip
+        - os: macos-latest
+          path: ~/Library/Caches/pip
+        - os: windows-latest
+          path: ~\AppData\Local\pip\Cache
+    steps:
+    - uses: actions/cache@v2
+      with:
+        path: ${{ matrix.path }}
+        key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
+        restore-keys: |
+         ${{ runner.os }}-pip-
+```
+
 ### Using pip to get cache location
 
 > Note: This requires pip 20.1+