configs/pjsip.conf.sample: Configuration section naming in pjsip.conf.sample needs a little clarification

There is a bit of nuance to how you name things in pjsip.conf. This is a documentation patch to at least clear it up a little for users.

Review: https://reviewboard.asterisk.org/r/3180/
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Merged revisions 407587 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@407588 f38db490-d61c-443f-a65b-d21fe96a405b