Augment documentation motivated by Martin's post on the mailing list.
Merge pull request #172 from bangerth/doc-fixes-9

Augment documentation motivated by Martin's post on the mailing list.
Fix an oversight in initializing the timer in step-32.
Fix an oversight in initializing the timer in step-40.
Improve documentation of TimerOutput.
Merge pull request #173 from bangerth/fix-step-32

Fix step 32