add some info into the README

README.md

 # Zoho Library
+
+### Development and testing
+
+To run the test you can use `rake spec` command in root folder of this project. 
+
+If you have a proxy and need to set it for testing you need to provide `SMS_PROXY` environment variables.
+The variable must in following format `http://<user>:<passowrd>@<host>:<port>` - any of the parts can be omitted if they are not necessary
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