Related to #2366 - make steady state runner work with whatever tolerances were prescribed.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19209 b5f69653-2bf5-0310-8201-b0dafb8e1405
Add a How To.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19210 b5f69653-2bf5-0310-8201-b0dafb8e1405