Added PELICAN_THEME_FOLDER docu in README

README.md

@@ -12,7 +12,8 @@ in the virtual environment your pelican site is developed in.
 
   - `GH_PAGES_BRANCH` (optional): override the default `gh-pages` deployment branch
   - `PELICAN_CONFIG_FILE` (optional): override the default `pelicanconf.py` config file    
-  - `PELICAN_CONTENT_FOLDER` (optional): 'override the default `content` content folder'        
+  - `PELICAN_CONTENT_FOLDER` (optional): override the default `content` content folder
+  - `PELICAN_THEME_FOLDER` (optional): setup the theme folder with `package.json` file, it is required if you need install node modules.   
   - `GITHUB_TOKEN`: (required) should be `${{secrets.GITHUB_TOKEN}}`, see [the workflow demo in the demo repository for an example of this][workflow_demo]. This secret is fulfilled by GitHub.
 
 ## Demo