DevDocs corrections part 1

Started reviewing the developer docs, finding lots of things to correct. I'll do more later, but please review this batch first so I know what, if anything, needs to be fixed moving forward - I'm not entirely sure on the markdownish format used.
How about we link instead to the Bitcoin.org Community page? https://bitcoin.org/en/community

For example, the sentence could say: "If you have questions, you can contact other developers through some of the resources listed on the [Community page](https://bitcoin.org/en/community)."