Chore: add dev setup information in contributing.md doc

[Dayvvo]

Added information about dev mode features namely:

• Multiple Jam Instances and their use in simulating collaborative transactions locally
• Block explorer and RPC terminal
• Dev setup page for accessing the above-named features

Partially resolves #724

[theborakompanioni]

Hey @Dayvvo!

Thanks for the PR.
There is some code in BitcoinQR.tsx I do not quite understand, as it has nothing todo with the linked issue or the description of your PR. There should already be a share button, when the navigator.share method is available.. Would you be able to explain your reasoning behind the change?

[Dayvvo]

Hello @theborakompanioni . Thanks for pointing that out!

You're right. Those changes were not supposed to be in this branch. Initially I was trying to attempt another feature. Sharing the QR image of an address along with the address with the share button and then raise an issue and a PR about that, but then I found that to not be possible with the navigator.share() implementation in the code and decided not to attempt that anymore. I believed those changes to not be present in this branch.

I have removed them and pushed only the changes related to the issue in the comment. Do take a look again. Thanks!