Add doc comment for exported variable

golint imposes the important requirement that all exported API components have a doc comment.

From a purely technical sense, there is no reason for the developer to have exported AppVersion, since it is not used in
other packages of the project and the project is exclusively a standalone application; not a reusable package.

However, there is maybe a little bit of semantic sense to exporting AppVersion. The deploy.sh script uses this line of
the code, so in a way it is "exported", even though it is used in an janky manner that does not care anything about Go's
export framework.

So the export may communicate that this line is an "API" of sorts and that modifying it must be done with care.

Author: per1234

main.go

@@ -17,6 +17,7 @@ import (
 	"time"
 )
 
+// AppVersion is the application version.
 const AppVersion = "1.3.0"
 
 var compileInfo string