Corrected DEVELOPER_FAQ.md

Besides some typos, I also want to point out the following change:

Line 5: maybe for a reason I do not understand, whoever wrote this skipped the item #2. Maybe it is an internal joke that I do not know about, maybe it is a different counting system or maybe he/she was just working with feverish haste. I like the number 2 and "dropped" the last sentence of #1 (which makes to me a valid item) to it.