Adding a VERSION.md file to document how the versioning system should work.

Author: ctesta01

VERSION.md

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+# Tabby2 Versioning System
+
+This document provides the specification for how the Tabby2 versioning system
+should be used.
+
+The purpose of the versioning system is to alert users of the Tabby2 web
+application to changes to Tabby2 which they may want to take note of.
+
+### Location of the Version Number
+
+The authority on the Tabby2 version number is specified in the
+`utilities/DESCRIPTION` file "Version:" line item. 
+
+This is done so that Tabby2 can render its version number in many places from
+one single source of authority.
+
+### Changelog
+
+The changelog providing brief descriptions of each version increment is 
+stored in `utilities/inst/Rmd/changelog.Rmd`.
+
+### Version Format
+
+The format of the Tabby2 version is given by three numbers separated by two
+periods, e.g. "Tabby2 Version 2.0.1"
+
+These version numbers are ordered in decreasing significance. 
+
+Changes to the first of these version numbers should indicate a major change in
+the scope of the project, such as changes in the funding source or
+methodological approach.
+
+Changes to the middle of these version numbers should indicate a significant
+release, indicating the successful completion of another round of Scientific
+Web Tool Clearance at the Centers for Disease Control and Prevention has been
+performed for Tabby2. 
+
+Changes to the last of these version numbers reflect smaller changes to the
+contents of Tabby2 to which the user should be alerted, such as the expansion
+and improvement of the underlying model, improvements to the user interface, or
+changes which affect the numbers depicted in downloadable outcomes from the
+application.