Document react template usage with lerna (#119)

templates/react/README.md

@@ -130,4 +130,19 @@ We recommend using https://github.com/sindresorhus/np.
 
 ## Usage with Lerna
 
-_to be completed_
+When creating a new package with TSDX within a project set up with Lerna, you might encounter a `Cannot resolve dependency` error when trying to run the `example` project. To fix that you will need to make changes to the `package.json` file _inside the `example` directory_.
+
+The problem is that due to the nature of how dependencies are installed in Lerna projects, the aliases in the example project's `package.json` might not point to the right place, as those dependencies might have been installed in the root of your Lerna project.
+
+Change the `alias` to point to where those packages are actually installed. This depends on the directory structure of your Lerna project, so the actual path might be different from the diff below.
+
+```diff
+   "alias": {
+-    "react": "../node_modules/react",
+-    "react-dom": "../node_modules/react-dom"
++    "react": "../../../node_modules/react",
++    "react-dom": "../../../node_modules/react-dom"
+   },
+```
+
+An alternative to fixing this problem would be to remove aliases altogether and define the dependencies referenced as aliases as dev dependencies instead. [However, that might cause other problems.](https://github.com/palmerhq/tsdx/issues/64)