docs: add Jest troubleshooting note for @react-three/cannon

packages/react-three-cannon/README.md

@@ -590,6 +590,20 @@ interface RaycastVehicleProps {
 - NaiveBroadphase is as simple as it gets. It considers every body to be a potential collider with every other body. This results in the maximum number of narrowphase checks.
 - SAPBroadphase sorts bodies along an axis and then moves down that list finding pairs by looking at body size and position of the next bodies. Control what axis to sort along by setting the axisIndex property.
 
+
+### Testing with Jest
+
+If Jest reports that it cannot find `@react-three/cannon`, the problem is usually related to the test environment rather than the runtime package itself.
+
+Because `@react-three/cannon` is commonly used in modern React/ESM setups, some Jest configurations may need additional module resolution or transform settings. If you are unit testing components that import physics hooks, consider one of these approaches:
+
+- configure Jest to handle ESM dependencies used by your React/Three stack
+- mock `@react-three/cannon` in tests that do not need real physics behavior
+- keep physics integration in higher-level tests and isolate pure logic into testable helper functions
+
+If this issue appears in your project, check your Jest resolver, transform settings, and test environment setup before assuming the package import itself is broken.
+
+
 #### Types
 
 - A dynamic body is fully simulated. Can be moved manually by the user, but normally they move according to forces. A dynamic body can collide with all body types. A dynamic body always has finite, non-zero mass.