docs: Update Readme with dependencies, guide for taskbar usage and building and debugging production

Merge pull request #440 from paritytech/luke-refactor-menu-and-no-close-minimise-window-for-taskbar-app

refactor: Update Fether menu for taskbar mode on non-macOS (add 'Quit', remove 'Close Window', remove 'Minimize') 

Fixed window size

fix: Fixes #421. Linux tray and dock icon not pixelated and Fether branding

fix: Fixes #442. Only run moveWindowUp when Fether window "frameless" and when showing window

Check for new Fether release & prompt user on startup

feat: Remove tray menu since can only left click tray icon on Windows so unable to toggle window show/hide as well