Contributing: Added G7 "Standard Methods"

CONTRIBUTING.md

@@ -105,6 +105,19 @@ DON'T:
 var bufferUtil = require('./util/buffer');
 ```
 
+### G7 - General: Standard Methods
+
+When possible, bitcore objects should have standard methods on an instance prototype:
+* `toObject` - A plain JavaScript object that can be JSON stringified
+* `toJSON` - A JSON stringified object of the instance
+* `toString` - A string representation of the instance
+* `toBuffer` - A hex Buffer
+
+These should have a matching static method that can be used for instantiation:
+* `fromJSON` - Should handle both JSON from `toJSON` and plain JavaScript object from `toObject`
+* `fromString` - Should be able to instantiate with output from `toString`
+* `fromBuffer` - Should likewise be able to instantiate from output from `toBuffer`
+
 ### E1 - Errors: Use bitcore.Errors
 
 We've designed a structure for Errors to follow and are slowly migrating to it.