Add instructions for testing changes to the typescript library from a…

… resource.

README.md

@@ -75,6 +75,19 @@ pip3 install \
 
 That ensures neither is accidentally installed from PyPI.
 
+For changes to the typescript library "@amazon-web-services-cloudformation/cloudformation-cli-typescript-lib" pack up the compiled javascript:
+
+```shell
+npm run build
+npm pack
+```
+
+You can then install this in a cfn resource project using:
+
+```shell
+npm install ../path/to/cloudformation-cli-typescript-plugin/amazon-web-services-cloudformation-cloudformation-cli-typescript-lib-1.0.1.tgz
+```
+
 Linting and running unit tests is done via [pre-commit](https://pre-commit.com/), and so is performed automatically on commit after being installed (`pre-commit install`). The continuous integration also runs these checks. Manual options are available so you don't have to commit:
 
 ```shell