Modified the install page so that it now shows:
- The table of contents at the beginning of the page. Had to modify the
  markdown a bit to make this appear (it only shows it if there's no first level
  heading in the md file).
- Added a new section to tell users where they can find the installers/binaries
  for older versions of Pidgin/Finch.

Ran dev-server.sh and verified content looked as intended