help: Get command syntax and examples

Usage:
  eg help --all
  eg help [COMMAND]
  eg help topic [TOPIC]

Description:
  Shows general help for eg, for one of its subcommands, or for a
  specialized topic.

Examples:
  Show help for eg
      $ eg help

  Show help for extended list of commands available in eg
      $ eg help --all

  Show help for the switch command of eg
      $ eg help switch

  Show which topics have available help
      $ eg help topic

  Show the help for the staging topic
      $ eg help topic staging

Differences from git help:
  eg help uses its own help system, ignoring the one from git help...except
  that eg help will call git help if asked for help on a subcommand it does
  not recognize.

  'git help COMMAND', by default, simply calls 'man git-COMMAND'.  The git
  man pages are really nice for people who are experts with git; they are
  comprehensive and detailed.  However, new users tend to get lost in a sea
  of details and advanced topics (among other problems).  'eg help COMMAND'
  provides much simpler pages of its own and refers to the manpages for
  more details.  The eg help pages also list any differences between the eg
  commands and the git ones, to assist interested users in learning git.

  If you simply want a brief list of available options and descriptions,
  you may also want to try running 'git COMMAND -h' (which differs from
  the two identical commands 'git COMMAND --help' and 'git help COMMAND').