Add example with reusable workflow and mention possibility of duplicate CI runs

Signed-off-by: Aleksei Khudiakov <[email protected]>

Author: Xerkus

README.md

@@ -64,7 +64,10 @@ Create `.github/workflows/continuous-integration.yml` file with following conten
 ```yaml
 name: "Continuous Integration"
 
-on: [push, pull_request]
+on:
+  pull_request:
+  push:
+    branches:
 
 jobs:
   matrix:
@@ -92,6 +95,29 @@ jobs:
           job: ${{ matrix.job }}
 ```
 
+Same can be achieved with our reusable workflow :
+
+```yaml
+name: "Continuous Integration"
+
+on:
+  pull_request:
+  push:
+    branches:
+
+jobs:
+  ci:
+    uses: laminas/workflow-continuous-integration/.github/workflows/[email protected]
+```
+
+> ### Duplicate CI runs
+>
+> When pull requests are opened from branches in the same repository CI pipeline could run twice for the same commit:
+> once when pushed to a branch and once when PR is opened. Workflow triggers could be adjusted to only run for
+> specific branches or to skip branches using simple glob patterns.
+> See [Events that trigger workflows](https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#running-your-workflow-only-when-a-push-to-specific-branches-occurs)
+> for more info.
+
 > ### actions/checkout not required
 >
 > The action will perform a checkout of the repository at the requested reference as part of its work, and therefore does not require the actions/checkout action as a preceding step.