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.

Added domain

This reverts commit 95687867d1.

Force hard linking the file

It was forgotten to add `-f` (force) option for `ln` in
95687867d1. This enables opening files
with the same names, but different contents, with a new NeoMutt
instance, after the previous is closed.

Hard link the file instead of copying

In the latest neomutt release (2022-04-08), neomutt/neomutt/pull/3267 is
merged. Neomutt doesn't overwrite files with zeros on closing anymore,
just unlinks it. Therefore, instead of copying, files can be hard
linked.