adding the ability to include a custom header (banner) on generated files (#334)

Author: kaolin

README.md

@@ -76,6 +76,20 @@ higher in your `tsconfig.json`. Note that the `eagerESModules` option from
 `relay-compiler` has no effect on the generated code if `module` is ES2015 or
 higher.* 
 
+#### Custom Headers
+
+If you need to add a custom header to generated files, perhaps for a custom linter
+or to get boilerplate license code in, that can be passed in also in compilerOptions 
+as `banner`:
+
+```json
+{
+  "compilerOptions": {
+    "banner": "/* © 2021 Example.org - @generated code */"
+  }
+}
+```
+
 ## Problems
 
 ### React Hot Loader

src/formatGeneratedModule.ts

@@ -90,7 +90,8 @@ ${nodeStatement}
 export default node;
 `;
 
-    const content = `/* tslint:disable */
+    const banner = compilerOptions.banner ? compilerOptions.banner + "\n" : "";
+    const content = `${banner}/* tslint:disable */
 /* eslint-disable */
 // @ts-nocheck
 ${hash ? `/* ${hash} */\n` : ""}