0.y.z compatibility note (#21)

* 0.y.z compatibility note

* Update README.md

Author: hudlow

README.md

@@ -9,6 +9,8 @@
 # IBM Cloud VPC Java SDK Version 0.4.3
 Java client library to interact with various [IBM Cloud VPC offerings](https://cloud.ibm.com/apidocs/vpc?code=java?).
 
+This SDK uses [Semantic Versioning](https://semver.org), and as such there may be backward-incompatible changes for any new `0.y.z` version.
+
 ## Table of Contents
 
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