accurate error description

Author: michaelsutton

consensus/core/src/errors/pruning.rs

@@ -30,7 +30,7 @@ pub enum PruningImportError {
     #[error("the pruning proof selected tip {0} at level {1} is not a parent of the pruning point on the same level")]
     PruningProofSelectedTipNotParentOfPruningPoint(Hash, BlockLevel),
 
-    #[error("the pruning proof selected tip {0} at level {1} blue score {2} <= 2M")]
+    #[error("the pruning proof selected tip {0} at level {1} blue score {2} < 2M and root is not genesis")]
     PruningProofSelectedTipNotEnoughBlueScore(Hash, BlockLevel, u64),
 
     #[error("provided pruning proof is weaker than local: {0}")]