fix(docs): add echo statements to display PROJECT_VERSION during documentation build

Author: oujago

.readthedocs.yml

@@ -14,10 +14,12 @@ build:
       # Copy the appropriate conf.py based on project name
       - |
         if [ "$PROJECT_VERSION" = "brainpy-version2" ]; then
+          echo "PROJECT_VERSION is: $PROJECT_VERSION"
           echo "Building brainpy-version2 documentation"
           mkdir -p docs_build
           cp -r docs_version2/* docs_build/
         else
+          echo "PROJECT_VERSION is: $PROJECT_VERSION"
           echo "Building standard brainpy documentation"
           mkdir -p docs_build
           cp -r docs/* docs_build/