Add basic build steps to README.md (#185)
Add basic build steps to README.md (#185)

Summary:
For those not familiar with android and iOS development practices, adding basic build instructions.
Pull Request resolved: https://github.com/facebook/Sonar/pull/185

Reviewed By: passy

Differential Revision: D8991468

Pulled By: jknoxville

fbshipit-source-id: 990dc1217c7b5275d143b915c1b4872b271f4c94

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