Fix some wiki typos and add more info regarding writing programs

Partially as a test of the new wiki setup, I fixed some things that I have been wanting to fix for a while. Here's the list:

- I fixed some typos on the new getting started page as well as in the Windows networking instructions (You don't want people going out to try to buy an [SD dard](https://github.com/mindboards/ev3dev/wiki/Getting-started-v2#step-1-get-a-microsd-dard)).
- I added some more text to the section on writing custom programs
- I added a note in the Windows networking instructions regarding multiple adapters

The wiki editing worked well, although some stuff didn't work (such as pushing it to my copy of the actual wiki, for example); I'll have to take a look at that. But at least now we can get some good wiki collaboration!
Sure. What do I do with the changes? Can I include other commits in an existing pull request?