add comment to test

Author: nschloe

test/test_volume_mesh.py

@@ -442,6 +442,7 @@ def test_extrude():
     assert abs(min(mesh.points[:, 0]) + 0.5) < tol
     assert abs(max(mesh.points[:, 1]) - 0.8) < tol
     assert abs(min(mesh.points[:, 1]) + 0.3) < tol
+    # Relax tolerance for debian, see <https://github.com/nschloe/pygalmesh/pull/47>
     assert abs(max(mesh.points[:, 2]) - 1.0) < 1.1e-3
     assert abs(min(mesh.points[:, 2]) + 0.0) < tol