Use nonlinear postsmoothing; Add notes

The notes refer to computational limits

src/one-body-sample.parset

@@ -15,11 +15,11 @@ useTNNMG = true
 refinements = 3
 
 [body]
-E = 3e2
+E = 3e3 # WARNING: At 1e5, this becomes tough; at 2e5 we have no convergence
 # "Most steels and rigid polymers when used within their design limits
 # (before yield) exhibit values of about 0.3"
 # -- http://en.wikipedia.org/wiki/Poisson's_ratio
-nu = 0.3
+nu = 0.3 # WARNING: From 0.39 on we have no convergence
 
 [solver]
 maxiterations = 1000000
@@ -38,7 +38,7 @@ nu2 = 1
 # And leaving off the postsmoothing is even better yet
 nu1 = 1
 mu = 4
-nu2 = 0
+nu2 = 1
 
 [localsolver]
 # Observation: Increasing this value yields noticeable additional