[Modules] Enable "module" command in shells

[Xavier D. <xav...@gm...>]

Dear All,

I found several users on Ubuntu having issues to enable the "module"
command after installing the environment-modules package [1][2][3][4].

On RedHat-like systems same profile scripts are run whether the shell
is executed as a login shell or not. This is not the case on
Debian-like system. So I have improved the documentation to explain
the extra step to apply to get the "module" command defined in
non-login shells:

https://modules.readthedocs.io/en/latest/INSTALL.html#enable-modules-in-shells

Regards,
Xavier

[1] https://askubuntu.com/q/1348222/1028641
[2] https://askubuntu.com/q/1275066/1028641
[3] https://askubuntu.com/q/1539132/1028641
[4] https://askubuntu.com/q/1490728/1028641