[DOC beta] First pass at additional TextSupport documentation, per #5065

An attempt to add some documentation in hopes of shedding more light on these methods. 
Should be inside triple backticks so it is presented as code.

If you pull down the website into a sibling folder to your emberjs codebase, you can boot the website and preview these docs. It seems like there is a lot of guessing here, but previewing this stuff locally is very easy.