Add action to publish Doxygen documentation as GH Page (#972)

* Add GH Action to publish Doxygen

* Add link in README

Author: sven-hoek

.github/workflows/doxygen-gh-pages.yml

@@ -0,0 +1,18 @@
+name: Doxygen GitHub Pages Deploy Action
+
+on:
+  push:
+    branches:
+      - main
+      - master
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - uses: DenverCoder1/doxygen-github-pages-action@v2.0.0
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          folder: doc/html

README.md

@@ -35,6 +35,8 @@ to visualize, record, replay and analyze state transitions.
 
 You can learn about the main concepts, the API and the tutorials here: https://www.behaviortree.dev/
 
+An automatically generated API documentation can be found here: https://BehaviorTree.github.io/BehaviorTree.CPP/
+
 If the documentation doesn't answer your questions and/or you want to
 connect with the other **BT.CPP** users, visit [our forum](https://github.com/BehaviorTree/BehaviorTree.CPP/discussions)