Add Versioning document.

Documents/Versioning.md

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+# NanaZip Versioning
+
+This document applies to all versions of NanaZip.
+
+## Version Format
+
+- Simple Version: `<Major>.<Minor> <Tag>`
+  - Example: `9.0 Preview 1`
+- Binary Version: `<Major>.<Minor>.<Build>.<Revision>`
+  - Example: `9.0.2654.0`
+
+## The rule for build and revision number
+
+The build number is the number of days since August 31, 2021 because the first 
+version of NanaZip is created and published on that day.
+
+The revision number is the number of releases releases in the day corresponding
+to the build number, and it counts from zero. So the first revision is 0 and 
+the second revision is 1.