update local serve instructions

Author: staeiou

README.md

@@ -18,9 +18,10 @@ See more info at https://academicpages.github.io/
 1. Clone the repository and made updates as detailed above
 1. Make sure you have ruby-dev, bundler, and nodejs installed: `sudo apt install ruby-dev ruby-bundler nodejs`
 1. Run `bundle clean` to clean up the directory (no need to run `--force`)
-1. Run `bundle install` to install ruby dependencies
+1. Run `bundle install` to install ruby dependencies. If you get errors, delete Gemfile.lock and try again.
 1. Run `bundle exec jekyll serve` to generate the HTML and serve it from localhost:4000
 
+
 # Changelog -- bugfixes and enhancements
 
 There is one logistical issue with a ready-to-fork template theme like academic pages that makes it a little tricky to get bug fixes and updates to the core theme. If you fork this repository, customize it, then pull again, you'll probably get merge conflicts. If you want to save your various .yml configuration files and markdown files, you can delete the repository and fork it again. Or you can manually patch.