Merge pull request #3185 from chrishalbert/bug/html-proof-reddit-errors

Add exclusion for reddit and updating contribution markdown.

CONTRIBUTING.md

@@ -47,7 +47,7 @@ If you're writing content, see the [style guide](./docs/styleguide.md) to help y
 
 ## Setting up your environment
 
-This site is powered by [Jekyll](https://jekyllrb.com/). Running it on your local machine requires a working [Ruby](https://www.ruby-lang.org/en/) installation with [Bundler](https://bundler.io/).
+This site is powered by [Jekyll](https://jekyllrb.com/). Running it on your local machine requires a working [Ruby](https://www.ruby-lang.org/en/) installation with [Bundler](https://bundler.io/) along with [npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm).
 
 Once you have that set up:
 

script/html-proofer

@@ -14,6 +14,7 @@ url_ignores = [
   %r{^https://guides\.github\.com/},
   %r{^https://help\.github\.com/},
   %r{^https://github\.com/},
+  %r{^https?://(www\.)?reddit\.com},
 ]
 
 HTMLProofer::Runner.new(