Don't include sdoc in Gemfile

[sheerun]

• Although generating Rails documentation for offline use can be useful, I don't see developers doing that. Using online documentation is much faster.
• It's worth noticing you can browse documentation of given Rails versions by appening Rails version to http://api.rubyonrails.org/ (example)
• For offline reference you can use for example Dash.app, there are also downloadable versions of Rails documentation.
• You can use rbenv-ctags plugin to browse both Rails, Ruby, and gems source code (and documentation) directly from editor.
• Generating documentation in per-project manner is waste of space and time.