NewRelicModule.m may not be added to build target

[shinji-newrelic]

I tried to integrate agent to iOS project but it didn't work correctly.

The reason was NewRelicModule.m is not added to build target.
In the README.md following step is described

add the ./rnnewrelic folder copied from the local workspace

However NewRelicModule.m is not added as build target if I added to select 'folder' in this step. I had to select 'files' instead of 'folder'.

Please update README.md to avoid this kind of mistake.

Thanks.