Improve user access to help information

Users have requested that we make it easier to access the farmOS user guide and documentation from within farmOS. This can be introduced as new "Help" menu and relevant page(s) in farmOS. Combined with the upcoming Setup UI, access to additional help information will make it easier for new users to learn & discover features and best practices when starting to use farmOS. This work will be broken into two parts:

First, simple integration with existing documentation:

• Introduce a Help menu with icon in easily-accessible area (near user menu, main menu, or Setup menu, TBD)
• Include links to farmOS.org user guide + documentation

After this first pass, continue improving help features with #205