Add Swift Package Manager (SPM) example (#159)

* Add Swift - SPM to examples

* Add link SPM example link to readme

* remove extra newline

* remove another extra newline

README.md

@@ -76,7 +76,7 @@ See [Examples](examples.md) for a list of `actions/cache` implementations for us
 - [Scala - SBT](./examples.md#scala---sbt)
 - [Swift, Objective-C - Carthage](./examples.md#swift-objective-c---carthage)
 - [Swift, Objective-C - CocoaPods](./examples.md#swift-objective-c---cocoapods)
-
+- [Swift - Swift Package Manager](./examples.md#swift---swift-package-manager)
 
 ## Cache Limits
 

examples.md

@@ -16,6 +16,7 @@
 - [Scala - SBT](#scala---sbt)
 - [Swift, Objective-C - Carthage](#swift-objective-c---carthage)
 - [Swift, Objective-C - CocoaPods](#swift-objective-c---cocoapods)
+- [Swift - Swift Package Manager](#swift---swift-package-manager)
 
 ## C# - NuGet
 Using [NuGet lock files](https://docs.microsoft.com/nuget/consume-packages/package-references-in-project-files#locking-dependencies):
@@ -373,3 +374,14 @@ When dependencies are installed later in the workflow, we must specify the same
     restore-keys: |
       ${{ runner.os }}-pods-
 ```
+
+## Swift - Swift Package Manager
+
+```yaml
+- uses: actions/cache@v1
+  with:
+    path: .build
+    key: ${{ runner.os }}-spm-${{ hashFiles('**/Package.resolved') }}
+    restore-keys: |
+      ${{ runner.os }}-spm-
+```