Show a main menu with options to the user.

Show a main menu to the user, the menu should have a "welcome" message, and then show the options the user can take. Up until now, there may be two options
1. introduce the command you want to send to ripgrep (something like that). The user input will go to this [line](https://github.com/KarlHeitmann/rg_wrapper/blob/8178db2cba9cfbb9141bb06887918004f859b40a/src/io.rs#L6)
2. Run the example command. You can repeat the command that is run [here](https://github.com/KarlHeitmann/rg_wrapper/blob/8178db2cba9cfbb9141bb06887918004f859b40a/src/io.rs#L6)