bug#31738: 27.0.50; Flymake manual doesn't mention that syntax checking is started in after-save-hook

[Michał Kondraciuk]

The Flymake manual says that syntax checking is started whenever

- ‘flymake-mode’ is started, unless ‘flymake-start-on-flymake-mode’
     is nil;
- a newline character is added to the buffer, unless
     ‘flymake-start-syntax-check-on-newline’ is nil;
- some changes were made to the buffer more than ‘0.5’ seconds ago


But it doesn't mention that Flymake also starts in 'after-save-hook.
Also, I think there should be an option to disable checking the buffer
on save.

In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2018-06-06 built on mkc
Repository revision: 4a51deb993d923767f0eddd4f350e636fe8d7c0b