Refine README

[luzpaz]

• Tweaking markdown to put the travisci badges in a table.
• Fix typos
• Adding hyperlinks to FreeCAD project
• Refining the Quickstart section to offer the option of using git clone as a way to quickly update the workbench code if it's been modified upstream
• grammar

Note: your CLA is extensive and I'd rather not share all those personal details. I don't need any attribution for my contribution so I propose that you cherrypick the commit (will erase any of my info) and merge the code as your own. You can use this ticket as my authorization to do so.

[luzpaz]

FYI, if this workbench is designed so that once it is installed it can git clone this repo... then it's possible to add this repo unofficially to the FreeCAD Addon Manager (as a custom repository).

Directions

1. Start FreeCAD
2. Tools > Addon Manager
3. Click Configure button
4. Add https://github.com/virtualsatellite/VirtualSatellite4-FreeCAD-mod
5. Save
6. Restart FC

Result: Everytime FC starts the addon manager will query the https://github.com/virtualsatellite/VirtualSatellite4-FreeCAD-mod repo and pull any new commits added (if it is behind master).