add: Mark content in files as being ready for commit

Description:
  eg add is provided for backward compatibility; it has identical usage and
  functionality as 'eg stage'.  See 'eg help stage' for more details.

Differences from git add:
  None.

See also
  Run 'git help add' for a comprehensive list of options available.
  eg add is designed to accept the same options as git add, and
  with the same meanings unless specified otherwise in the above
  "Differences" section.