Update README.md (#84)

* Update README.md

Add extra step to work around ruby 3.0 issue with Jekyll

Author: saparikh

README.md

@@ -8,6 +8,7 @@ You can build and view it locally using [Jekyll](https://jekyllrb.com/).
 gem install bundler jekyll
 cd <local repository directory>
 bundle install
+bundle add webrick
 bundle exec jekyll serve
 ```