Add instructions for installing and using Git in VSCode

[rantahar]

Adds a git in VSCode page and refers to that in installation options 2 and 4.

See issue #300

• This makes the instructions more specific to VSCode. The terminal instructions are more general, but require using the terminal a bit more.
• Review:
  • Is this the right choice? Should we point everyone to the git-for-terminal page instead and edit it a bit?
  • Does the content flow well? Spelling?

[bast]

• minor: duplicate label git-configuration
• the two pages differ in 50% (so i understand that it was a pain to make it generic) but also overlap in 50% (big risk of diverging changes in future) -> i would suggest solving it with one page and tabs so that we only change the common stuff in one place in future
• but maybe that makes it more confusing for learners and in this case we should abstract the common stuff into a new page instead of repeating

[rantahar]

Tabs are a good idea, why didn't I think of that :)

The biggest differences are between Windows (most setup done while installing) and the rest (config in terminal). Some setup is not needed for VSCode, but it's not that different.