[README] Document need to output ES modules

Closes #40.

Author: alloy

README.md

@@ -15,6 +15,10 @@ Add the package to your dev dependencies:
 yarn add relay-compiler-language-typescript --dev
 ```
 
+## Configuration
+
+### relay-compiler
+
 Then configure your `relay-compiler` script to use it, like so:
 
 ```json
@@ -25,7 +29,7 @@ Then configure your `relay-compiler` script to use it, like so:
 }
 ```
 
-This is going to store all artifacts in a single directory, which you also need to instruct the Babel plugin to use:
+This is going to store all artifacts in a single directory, which you also need to instruct `babel-plugin-relay` to use in your `.babelrc`:
 
 ```json
 {
@@ -35,6 +39,29 @@ This is going to store all artifacts in a single directory, which you also need
 }
 ```
 
+### TypeScript
+
+Also be sure to configure the TypeScript compiler to transpile to `es2015` modules and leave transpilation to `commonjs` modules up to Babel with the following `tsconfig.json` settings:
+
+```json
+{
+  "compilerOptions": {
+    "target": "es2015",
+    "module": "es2015"
+  }
+}
+```
+
+The reason for this is that `tsc` would otherwise generate code where the imported `graphql` function is being namespaced (`react_relay_1` in this example):
+
+```js
+react_relay_1.createFragmentContainer(MyComponent, react_relay_1.graphql `
+  ...
+`);
+```
+
+…and this makes it impossible for `babel-plugin-relay` to find the locations where the `graphql` function is being used.
+
 ## Examples
 
 You can find a copy of the Relay