Add documentation about specific scenarios that are not supported by …

…the codemod

packages/mui-codemod/README.md

@@ -672,6 +672,19 @@ export default App;
 npx @mui/codemod v5.0.0/jss-to-tss-react <path>
 ```
 
+The following scenarios are not currently handled by this codemod and will be marked with a
+"TODO jss-to-tss-react codemod" comment:
+
+- If the hook returned by `makeStyles` (e.g. `useStyles`) is exported and used in another file,
+  the usages in other files will not be converted.
+- Arrow functions as the value for a CSS prop will not be converted. Arrow functions **are**
+  supported at the rule level, though with some caveats listed below.
+- In order for arrow functions at the rule level to be converted, the parameter must use object
+  destructuring (e.g. `root: ({color, padding}) => (...)`). If the parameter is not destructured
+  (e.g. `root: (props) => (...)`), it will not be converted.
+- If an arrow function at the rule level contains a code block (i.e. contains an explicit `return`
+  statement) rather than just an object expression, it will not be converted.
+
 You can find more details about migrating from JSS to tss-react in [the migration guide](https://mui.com/guides/migration-v4/#2-use-tss-react).
 
 #### `link-underline-hover`