Adding some additional explanatory comments based on code review feed…

…back

version.go

@@ -47,6 +47,10 @@ func init() {
 			if d.Path == mainPackage {
 				driverName = defaultDriverName
 				driverVersion = d.Version
+				// If there's a replace directive in play for the gocql package
+				// then use that information for path and version instead.  This
+				// will allow forks or other local packages to clearly identify
+				// themselves as distinct from mainPackage above.
 				if d.Replace != nil {
 					driverName = d.Replace.Path
 					driverVersion = d.Replace.Version