Add Support for POP3 Notification

add umbc.edu domain

(README.md) put keyboard shortcuts in <kbd> tag

Update domains.csv

pass: add feature to optionally add a prefix

Fix: find & case-insensitive filesystem

On case-insensitive filesystem,
`inbox` and `Inbox` are the same path.
Running `find Inbox inbox [expr]` will print twice the same information.

Use shell glob instead:
`find` will descend into path `inbox`,
ignoring letter cases, only once.

Fix #828.

added domain for freedom.nl

fix notifications when the Xorg process is just X

To close #845 :

I added the `-x` flag to prevent the regex from matching on _every_ pro-
cess name containing an `X`.

Because I'm not entirely sure about portability (does every `pgrep` va-
riant support that flag), I didn't push this directly.

So what do you think @LukeSmithxyz ?

Add purelymail.com to domains.csv

added encryption shortcut in neomutt interface description

Clearer description of encryption shortcut.