Reorder usage examples for brew help

- Reorder listed commands to better reflect a typical workflow (search,
  then query for details via `info` and friends, then install, later
  update and upgrade, at last maybe uninstall).
- Remove niche `pin` and `unpin` commands.
- Drop `--env` in the Troubleshooting section.

And use `/REGEX/` instead of `/PATTERN/` to be clearer what is expected.

Closes #177.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>

Library/Homebrew/cmd/help.rb

 HOMEBREW_HELP = <<-EOS
 Example usage:
+  brew search [TEXT|/REGEX/]
   brew (info|home|options) [FORMULA...]
   brew install FORMULA...
-  brew uninstall FORMULA...
-  brew search [TEXT|/PATTERN/]
-  brew list [FORMULA...]
   brew update
   brew upgrade [FORMULA...]
-  brew (pin|unpin) [FORMULA...]
+  brew uninstall FORMULA...
+  brew list [FORMULA...]
 
 Troubleshooting:
+  brew config
   brew doctor
   brew install -vd FORMULA
-  brew (--env|config)
 
 Brewing:
   brew create [URL [--no-fetch]]