Add remotes for ggb

[David Rügamer]

Hi Jacob,

great package! One minor suggestion: As long as ggb stays on Github, maybe you could add a remotes line for ggb to the DESCRIPTION file, like this:

Remotes: jacobbien/ggb

This way, the installation of trac using install_github should directly search for ggb on Github, not on CRAN. Otherwise users of trac will get an error

Error: Failed to install 'trac' from GitHub:
  (converted from warning) package ‘ggb’ is not available for this version of R

when trying to install trac (and some users might not know where to search for ggb then). Alternatively: Add one line of explanation to your README.

Awesome work!
David

[Jacob Bien]

Thank you, @davidruegamer for raising this issue and providing the solution! Fixed in 8b2c5ba.