docs: Add note on types to upgrade guide

docs/docs/Usage/upgrade-guide.md

@@ -47,3 +47,6 @@ The same is true for `postOnce()`, `deleteOnce()` etc.
 ### `sandbox()` method removed
 
 This was principally used when mocking node-fetch referenced as a local variable. Given that `fetch` is now available as a native global it's less useful and has been removed. If necessary to mock a local instance of node-fetch use [`.fetchHandler`](/fetch-mock/docs/API/mocking-and-spying#fetchhandler)
+
+### Types completely written
+There are many changes, both in the naming and structuring of types. Refer to the errors generated by your toolchain to update these.