docs: add instructions for removing fish help abbreviations

Add documentation showing how to erase the fish abbreviations for
--help and -h, since the dash-prefixed names make removal non-obvious.
The key is using -- before the abbreviation name to prevent fish from
interpreting it as a flag.

Closes #3536

CHANGELOG.md

@@ -1,6 +1,10 @@
 # unreleased
 
 
+## Other
+
+- Add instructions for removing fish help abbreviations to README, see #3655 (@claw-explorer). Closes #3536
+
 ## Features
 
 - Preserve `--diff` change markers and snip separators when `--plain` is set. Closes #3630, see #3643 (@mvanhorn)

README.md

@@ -244,6 +244,15 @@ abbr -a --position anywhere -- --help '--help | bat -plhelp'
 abbr -a --position anywhere -- -h '-h | bat -plhelp'
 ```
 
+To remove these abbreviations later:
+
+```fish
+abbr -e -- --help
+abbr -e -- -h
+```
+
+The `--` before the abbreviation name is required because `--help` and `-h` start with dashes, which would otherwise be interpreted as flags to `abbr` itself.
+
 This way, you can keep on using `cp --help`, but get colorized help pages.
 
 Be aware that in some cases, `-h` may not be a shorthand of `--help` (for example with `ls`). In cases where you need to use `-h`