Summary:
Change iOS to Objective C, reference which file is being updated
- Clarifies how to update iOS if using objective C for flipper network plugin
## Changelog
- renamed iOS to ObjC for flipper network plugin setup
- specified which iOS file to modify for flipper network plugin setup
Pull Request resolved: https://github.com/facebook/flipper/pull/2595
Test Plan:
Imported from GitHub, without a `Test Plan:` line.
|[Site Preview: flipper](https://our.intern.facebook.com/intern/staticdocs/eph/D29662605/V2/flipper/)
Reviewed By: passy
Differential Revision: D29662605
Pulled By: nikoant
fbshipit-source-id: acdc8bba73900c19500fc91f8a275930c51d73ad
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