aitools/README: fix install command shape

The README listed `databricks aitools install [skill-name]`, but the command
is `Use: "install"` with `cobra.NoArgs` and uses `--skills <name>` for
specific skills. Match the actual command.

Co-authored-by: Isaac

Author: simonfaltum

aitools/README.md

@@ -4,7 +4,7 @@
 
 ## Commands
 
-- `databricks aitools install [skill-name]`
+- `databricks aitools install` (use `--skills <name>[,<name>...]` to install specific skills)
 - `databricks aitools update`
 - `databricks aitools uninstall`
 - `databricks aitools list`