docs: more warn on auto-complete migrate

See toolshed/abra#553

docs/abra/upgrade.md

@@ -82,6 +82,10 @@ And test things work.
 * Auto-completion for `abra` is handled differently now. See `abra autocomplete
   --help` for more. The full help output is available for each specific shell,
   e.g. `abra autocomplete zsh --help`. It is now generated on the fly.
+  **WARNING**: you'll need to REMOVE your pre `v0.10.x` `abra` auto-complete
+  config for the new auto-complete to work. Check your `$SHELL` configuration
+  file (e.g. `.zshrc` for Zsh). See
+  [`#553`](https://git.coopcloud.tech/toolshed/abra/issues/553) for more.
 
 * Several commands now make use of the `--chaos/-C` commands, such as `abra app
   ps` and `abra app cp`. See `--help` for more.