runtime: make error clearer

make the error clearer and state that images created by other tools
might not be visible to Podman when it overrides the graph driver.

Closes: containers#13970

[NO NEW TESTS NEEDED]

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

libpod/runtime.go

@@ -1058,7 +1058,7 @@ func (r *Runtime) mergeDBConfig(dbConfig *DBConfig) {
 	if !r.storageSet.GraphDriverNameSet && dbConfig.GraphDriver != "" {
 		if r.storageConfig.GraphDriverName != dbConfig.GraphDriver &&
 			r.storageConfig.GraphDriverName != "" {
-			logrus.Errorf("User-selected graph driver %q overwritten by graph driver %q from database - delete libpod local files to resolve",
+			logrus.Errorf("User-selected graph driver %q overwritten by graph driver %q from database - delete libpod local files to resolve.  May prevent use of images created by other tools",
 				r.storageConfig.GraphDriverName, dbConfig.GraphDriver)
 		}
 		r.storageConfig.GraphDriverName = dbConfig.GraphDriver