Changes in DEVELOPER_FAQ.md

Corrected a few typos and

in line 5: maybe for a reason I do not understand, whoever wrote this
skipped the item #2. Maybe it is an internal joke and I broke it. However,
as I really do like the number 2, I "dropped" the last sentence of the
first item to a new item (numbered 2).
Merge pull request #9402 from mafagafogigante/developer-faq

Changes in DEVELOPER_FAQ.md