Add webpage on developer meetings

This adds a page on developer meetings under the notes section on the GS2 website. This is really just a link to information that’s already available on the wiki.

This PR won’t build automatically, so to see what the page looks like you need to do the following locally:

1. Checkout the branch: git checkout feature/links-to-dev-meetings

2. Make the documentation: make doc

3. Open the local html file in a browser: firefox docs/html/index.html

4. Click the Notes tab on the top, the GS2 Developer Meetings on the sidebar.