add commet to coverage.sh

Author: oscarbenjamin

bin/coverage.sh

@@ -1,7 +1,13 @@
 #!/bin/bash
 #
 # Note: cython's Cython/Coverage.py fails for pyx files that are included in
-# other pyx files. A patch to the file is needed:
+# other pyx files. This gives the following error:
+#
+#   $ coverage report -m
+#   Plugin 'Cython.Coverage.Plugin' did not provide a file reporter for
+#   '.../python-flint/src/flint/fmpz.pyx'.
+#
+# A patch to the file is needed:
 #
 #  --- Coverage.py.backup   2022-12-09 17:36:35.387690467 +0000
 #  +++ Coverage.py 2022-12-09 17:08:06.282516837 +0000