Summary:
Fixes the Flipper-RSocket podspec similar to the [RSocket podpec](https://github.com/facebook/flipper/pull/1438) to exclude the .md and .txt files from the compilation, which is throwing a warning.
Removal of these warnings:
```
warning: no rule to process file '<redacted>/ios/Pods/Flipper-RSocket/rsocket/benchmarks/CMakeLists.txt' of type 'text' for architecture 'arm64' (in target 'Flipper-RSocket' from project 'Pods')
warning: no rule to process file '<redacted>/ios/Pods/Flipper-RSocket/rsocket/benchmarks/README.md' of type 'net.daringfireball.markdown' for architecture 'arm64' (in target 'Flipper-RSocket' from project 'Pods')
warning: no rule to process file '<redacted>/ios/Pods/Flipper-RSocket/rsocket/README.md' of type 'net.daringfireball.markdown' for architecture 'arm64' (in target 'Flipper-RSocket' from project 'Pods')
```
## Changelog
Fix Flipper-RSocket podspec to exclude .txt and .md files from being included in the compilation
Pull Request resolved: https://github.com/facebook/flipper/pull/2079
Reviewed By: passy
Differential Revision: D27230095
Pulled By: priteshrnandgaonkar
fbshipit-source-id: 0876901aaad1a3b4e8093ed4ccf1cc845e18032a
025b51a284