(cake-contribGH-704) added `git fetch --prune --unshallow"

to the list of steps and explained why that is needed.

docs/input/docs/ci-systems/github.md

@@ -12,7 +12,12 @@ Description: Building with GitHub Actions
 
 * `actions/checkout`
 
- The default for `fetch-depth` is `1` - this currently does not work with `GitVersion`. Set `fetch-depth: 0` to fetch all history for all branches.
+ The default for `fetch-depth` is `1` - this currently does not work with `GitVersion`. 
+ Additionally information on different tags and branches is needed on some occasions 
+ (like building from a tag which does happen when releasing a new version.)
+
+ Therefore it is required to "unshallow" the checked out repository by adding a manual 
+ step: `git fetch --prune --unshallow`
 
 ## Example Config
 
@@ -27,9 +32,11 @@ jobs:
  runs-on: windows-latest
 
  steps:
- - uses: actions/checkout@v2.2.0
- with:
- fetch-depth: 0
+ - name: Checkout the repository 
+ uses: actions/checkout@v2
+
+ - name: Fetch all tags and branches
+ run: git fetch --prune --unshallow
 
  - name: Cache Tools
  uses: actions/cache@v2