Update getting-started.md (#6006)
Update getting-started.md (#6006)

I just tested this turorial and got stuck, didnt manage to see my changes in the test project. Because i didn´t bump it initially.
I prepose:
Add: "First time you do this you need to bump the code to GitHub to generate a tag." 
Changed the "cloud icon" to Github button. (wrongly looked for a button looking like a cloud)
Microsoft/pxt,Microsoft/pxt,Microsoft/pxt,Microsoft/pxt,Microsoft/pxt