Add a note mentioning spam waves to the Autoflagging Preferences page

[CoconutMacaroon]

Rationale

Autoflags for spam waves specifically are automatically cast for users with the Checkbox to enable MS flagging, regardless of their autoflagging preferences (or lack thereof). This should be documented somewhere, as it is bad practice to cast flags without giving them a heads-up first, especially as it isn't explained anywhere.

Spam wave autoflagging has also been discussed multiple times in CHQ.

TODO

• [x] Write text explaining the existence of spam wave autoflagging
• [x] Add a link to more details on what spam waves are
• [ ] Test these changes (I haven't yet)

[CoconutMacaroon]

Once completed, this should fix #924

[Spevacus]

I'd adjust the full blurb a bit more. Specifically, I'd change it to:

If the above checkbox is checked and you have either or both no valid autoflagging preferences or no valid and enabled autoflagging conditions, then autoflagging for your account will be disabled and only manual flagging will be functional.

There is one exception to this. By checking the above box, autoflags may be automatically cast from your account for spam waves, regardless of your autoflagging settings. Spam waves are a manual tool used sparingly by Metasmoke admins to fight waves of spam or abusive content, and can be configured to cast the necessary number of spam flags to instantly delete posts that meet specific criteria.

[CoconutMacaroon]

I tried to test these changes. Unfortunately, metasmoke wants me to authenticate with SE before showing that text, and I had trouble doing that. As a result, I have not successfully tested this.