add content on versioning approach.

VERSIONING.md

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+Versioning
+=====
+
+For releases we will follow semantic versioning approach. (http://semver.org/)
+
+Semantic Versioning
+===================
+
+Semantic versioning is a very simple scheme built around the X.Y.Z-buildNo concept (for example 2.6.0-x or 2.6.0-BUILD-SNAPSHOT):
+
+    Increment Z when you fix something
+    Increment Y when you add a new feature
+    Increment X when you break backwards-compatibility or add major features
+    Use the buildNo to differentiate different builds off the same branch, and to differentiate between development, test and production builds.
+    
+Version structure
+
+{number}.{release_type}
+
+where {number} is further broken down as {major}.{minor}.{micro}.
+
+Examples:
+
+    1.0.0.BUILD-SNAPSHOT
+    1.0.0.M1
+    1.0.0.RC1
+    1.0.0.RELEASE
+
+Number semantics
+
+major/minor/micro semantics may have some variance across projects but in general this is what we mean.
+
+In general:
+
+    a major version suggests many significant new features, an associated marketing campaign, and possible breaking of backward compatibility.
+    a minor version may also contain serious new features, but should not break compatibility. You can expect minor releases every 1-3 months.
+    a micro version typically contains many bug fixes and improvements and perhaps several smaller new features. You can expect micro version approximately every 5-20 days (depending on bugs or suggested improvements).
+
+Order matters
+
+Notice that the following sequence of versions is in ordered ascending both alphabetically and toward GA:
+
+    1.0.0.BUILD-SNAPSHOT
+    1.0.0.M1
+    1.0.0.RC1
+    1.0.0.RELEASE
+    
+What You Should Install Where
+
+As a rule of thumb …
+
+    Snapshot or Milestone versions should only be installed on dev boxes and integration environments. They shouldn’t be deployed to any of the dedicated test environments.
+    Release candidates should be installed in the dedicated test environments. In an emergency, a release candidate can be installed into the production environment.
+    Production releases can be installed anywhere - and they are the only kind of build that should be installed into the production environment.