Fix small typo in managing.tex

The "Simple Configuration File" section loads examples/configs/sample.conf but
then later explains that it loaded "the mongrel2.conf into it".

Fix the explanation.
Suggest some grammatical changes to managing.tex

Adjust a few sentences that looked odd on first read.
Merge pull request #176 from cpick/typo

Suggest some grammatical changes and fix typos in managing.tex