Add page(s) for indentation #107
Description
Similar to the split proposed in #106, we shoud have a guide page for all things indentation based on the the forum post by @keith-hall: https://forum.sublimetext.com/t/everything-you-n-ever-wanted-to-know-about-indentation-in-st3/26207
It should explain the basic workings of the indentation feature, how it is configured and refer to the tmPreferences reference page for details on the file format and individual supported keys.