test: Add remark on how to regenerate tests

Dockerfile

@@ -33,3 +33,8 @@ COPY test /TypeStrong/ts-loader/test
 # build and run tests with:
 # docker build -t ts-loader . 
 # docker run -it ts-loader yarn test
+
+# regenerate comparison-tests with:
+# docker build -t ts-loader .
+# yarn build
+# docker run -v $(pwd):/TypeStrong/ts-loader -it ts-loader yarn run comparison-tests --save-output