Add 2FA acronym for ease of search

Use the acronym to describe the protocol.

Using-Mastodon/2FA.md

@@ -1,10 +1,10 @@
-# Two Factor Authentication
+# Two Factor Authentication (2FA)
 
-Two Factor Authentication is a security mechanism that requires you to enter a computer generated code from your phone every time you log into Mastodon.
+Two Factor Authentication (2FA) is a security mechanism that requires you to enter a computer generated code from your phone every time you log into Mastodon.
 
 We highly recommend that you set up two factor authentication as it prevents malicious users from logging into your account if they obtain your password.
 
-The two factor auth protocol used by Mastodon is an implementation of [RFC 6238](https://tools.ietf.org/html/rfc6238), TOTP: Time-Based One-Time Password Algorithm.
+The 2FA protocol used by Mastodon is an implementation of [RFC 6238](https://tools.ietf.org/html/rfc6238), TOTP: Time-Based One-Time Password Algorithm.
 
 ## Warning