Fix some of the grammar issues in doc/tex/qos.tex.

(closes issue #14049)
Reported by: kshumard
Patches:
      doc.tex.qos.tex.patch uploaded by kshumard (license 92)
      (Slight modifications by seanbright)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@163037 65c4cc65-6c06-0410-ace0-fbb531ad65f3