Reduce error to debug and add notes

Signed-off-by: Michael Carroll <[email protected]>

dartsim/src/SDFFeatures.cc

@@ -306,8 +306,11 @@ static ShapeAndTransform ConstructPlane(
 static ShapeAndTransform ConstructHeightmap(
     const ::sdf::Heightmap & /*_heightmap*/)
 {
-  gzerr << "Heightmap construction from an SDF has not been implemented yet "
-         << "for dartsim.\n";
+  // TODO(mjcarroll) Allow dartsim to construct heightmaps internally rather
+  // than relying on the physics consumer constructing and attaching:
+  // https://github.com/gazebosim/gz-physics/issues/451
+  gzdbg << "Heightmap construction from an SDF has not been implemented yet "
+        << "for dartsim. Use AttachHeightmapShapeFeature to use heightmaps.\n";
   return {nullptr};
 }
 
@@ -317,8 +320,11 @@ static ShapeAndTransform ConstructMesh(
 {
   // TODO(MXG): Look into what kind of mesh URI we get here. Will it just be
   // a local file name, or do we need to resolve the URI?
-  gzerr << "Mesh construction from an SDF has not been implemented yet for "
-         << "dartsim.\n";
+  // TODO(mjcarroll) Allow dartsim to construct meshes internally rather
+  // than relying on the physics consumer constructing and attaching:
+  // https://github.com/gazebosim/gz-physics/issues/451
+  gzdbg << "Mesh construction from an SDF has not been implemented yet for "
+        << "dartsim. Use AttachMeshShapeFeature to use mesh shapes.\n";
   return {nullptr};
 }