Home: Add a brief description of the behavior (#794)

* Home: Add a brief description of the behavior

I could not find this information anywhere and think it is quite important for understanding how to use and configure the proxy for different use cases.

(Especially the Ajax part is not mentioned anywhere else I believe.)

I tried to keep it general enough so that it won't need updating often yet useful enough to have good value :)

* Update docs/0_index.md

Co-authored-by: Joel Speed <Joel.speed@hotmail.co.uk>

Co-authored-by: Joel Speed <Joel.speed@hotmail.co.uk>