feat: create shell module (#2329)

* Add the shell module

This module allows to quickly identify which shell is currently used, in case someone frequently switches between them.

* Updated documentation with shell module.

Co-authored-by: mro <mro@fedorabox.localdomain>

src/configs/mod.rs

@@ -42,6 +42,7 @@ pub mod purescript;
 pub mod python;
 pub mod ruby;
 pub mod rust;
+pub mod shell;
 pub mod shlvl;
 pub mod singularity;
 mod starship_root;