docs: note hooks require mise activate

docs/hooks.md

@@ -1,6 +1,8 @@
 # Hooks <Badge type="warning" text="experimental" />
 
-You can have mise automatically execute scripts when it runs. The configuration goes into `mise.toml`.
+You can have mise automatically execute scripts during a `mise activate` session. You cannot use these
+without the `mise activate` shell hook installed in your shell—except the `preinstall` and `postinstall` hooks.
+The configuration goes into `mise.toml`.
 
 ## CD hook