This command allows the inclusion of initialization commands
from other files. For example, I place all of my aliases in
~/.mail_aliases so that I can make my
~/.muttrc readable and keep my aliases private.
If the filename begins with a tilde (``~''), it will be expanded to the path of your home directory.
If the filename ends with a vertical bar (|), then filename is
considered to be an executable program from which to read input (eg.