Introduce react-native example

[TheRealNate]

[linegel]

Checked example on with both android (10 on simulator, 11 on real device) and ios (14.5 on simulator, 14.7.1 on real device) builds and works well!

Though still, there is the same question, discussed for as long, as RN exists: what is recommended way to work with Meteor backend from RN client. There are strong pros and cons about the way @TheRealNate made it in this PR. In many cases, it would be preferred to use client-bundler by @Urigo just because it could bundle additional libraries from the atmosphere which in many cases are required for the proper functioning of backend with a client without undefined behavior.

[linegel]

@TheRealNate also please add the description of the repo to README as described in How to add your example? section. Those points

• Create a PR including it in this README
• Make sure you are using the latest Meteor
• Required fields: Repository, Why, Stack, Last Updated At, and Meteor Version.

Will be important and useful for anyone who will be researching examples of Meteor usage