Buffalo Plugins documentation is outdated

[tatang26]

As title says, this doc topic is outdated due the following:

• It still indicating to install a deprecated library: github.com/gobuffalo/buffalo-plugins
• Writing a Plugin section are not clear. pe,$ buffalo generate plugin github.com/foo/buffalo-bar doesn't work and is needed to update the content of generated files

[sio4]

Agree! I guess it could be/should be updated once the progress on CLI by @paganotoni is done.