fix(docs): add echo statements for DOC_BUILD_VERSION during documentation build

Author: oujago

.readthedocs.yml

@@ -15,14 +15,27 @@ build:
       - |
         if [ "$PROJECT_VERSION" = "brainpy-version2" ]; then
           echo "PROJECT_VERSION is: $PROJECT_VERSION"
+          echo "DOC_BUILD_VERSION is: $DOC_BUILD_VERSION"
           echo "Building brainpy-version2 documentation"
           mkdir -p docs_build
           cp -r docs_version2/* docs_build/
         else
+          echo "DOC_BUILD_VERSION is: $DOC_BUILD_VERSION"
           echo "PROJECT_VERSION is: $PROJECT_VERSION"
           echo "Building standard brainpy documentation"
           mkdir -p docs_build
           cp -r docs/* docs_build/
+        
+        if [ "$DOC_BUILD_VERSION" = "v2" ]; then
+          echo "DOC_BUILD_VERSION is: $DOC_BUILD_VERSION"
+          echo "Building brainpy-version2 documentation"
+          mkdir -p docs_build
+          cp -r docs_version2/* docs_build/
+        else
+          echo "DOC_BUILD_VERSION is: $DOC_BUILD_VERSION"
+          echo "Building standard brainpy documentation"
+          mkdir -p docs_build
+          cp -r docs/* docs_build/
         fi
 
 # Build documentation using the copied conf.py