docs: update document according to the recent update

build-docs.sh

@@ -2,19 +2,32 @@
 # Description:
 #   This script is used to build the CEPCSW docs.
 
+function install-sphinx() {
+    if [ ! -d "venv" ]; then
+        python -m venv venv
+        source venv/bin/activate
+        # pip install -r requirements.txt
+        pip install sphinx-rtd-theme myst-parser
+    else
+        source venv/bin/activate
+    fi
+}
+
 function check-sphinx() {
     which sphinx-build >& /dev/null
 }
 
 function run-build-docs() {
-    pushd docs
     make html
-    popd
 }
 
+pushd docs
+install-sphinx
+
 if check-sphinx; then
     run-build-docs
 else
     echo "Please setup sphinx before build the docs. " 1>&2
     exit -1
 fi
+popd