add link to assemble.io repo

[Jon Schlinkert]

for anything related to docs

[assemblebot]

@jonschlinkert Thanks for the issue! If you're reporting a bug, please be sure to include:

• The version of assemble you are using.
• Your assemblefile.js (This can be in a gist)
• The commandline output. (Screenshot or gist is fine)
• What you expected to happen instead.

[Jon Schlinkert]

moving to #5