Add some help inside the Home tab page

To see what you can do inside a tab page, you need to look at the source code of the application. Because there is not a single hint on what the application can do.

Take a look at the source code on `./src/ui/home.rs`, there are no actions the user can take here. Only the global actions described on the function `selection_menu_handler` (HINT: use rg explorer to find where this function is defined ;) ).

To solve this issue, create a new function on `./src/ui/home.rs` so when the user hits "?", it will display a widget showing him some general help: what keys he must press to go to each tab, what this project does, and what is the purpose of each tab.

You can inspire yourself by seeing how the handler `action_edit` function works. Use rg_explorer to find in which place this function is defined, and where it is used. Try to follow this pattern.