Fix typo.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19236 b5f69653-2bf5-0310-8201-b0dafb8e1405
Comment on steady state tolerances

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19238 b5f69653-2bf5-0310-8201-b0dafb8e1405