Add some help inside the Home tab page

Same as #2 , but for [src/ui/sub_search.rs](https://github.com/KarlHeitmann/rg_explorer/blob/master/src/ui/sub_search.rs) file

This file will show the user a new tab where he can input a new search term, and when he hits the `enter` key, it will perform a new rip grep search over the list of matched files of the original search term.

The new rip grep search will call recursively the function [rip_grep_wrapper](https://github.com/KarlHeitmann/rg_explorer/blob/master/src/wrapper.rs#L59), but will provide slightly different parameters to the function, and it will _borrow_ the terminal instance. This is the power of [fractals](https://en.wikipedia.org/wiki/Mandelbrot_set)