add a section about parallel tests (#807)

Author: KazuCocoa

ios_tests/readme.md

@@ -29,3 +29,4 @@ Finished in 1 min 57 secs
 ### Tips for parallel 
 
 - https://github.com/grosser/parallel_tests
+   - Usage: https://github.com/appium/ruby_lib_core#run-parallel-tests-with-parallel_tests-gem

readme.md

@@ -74,6 +74,8 @@ gem install --no-rdoc --no-ri appium_lib
 # Load Pry
 `Pry.config.pager = false` is set if you have no `.pryrc` files and `Pry` is defined.
 
+# Run tests in parallel
+This repository has examples for running tests in parallel. Read [ios_tests](https://github.com/appium/ruby_lib/tree/master/ios_tests) to see them.
 
 # Contribute
 ## How to add new commands for `driver`