Submit PR to get on Metamask

[treeder]

Looks like we could submit a PR changing these files:

https://github.com/MetaMask/metamask-extension/blob/develop/docs/adding-new-networks.md

[r-gochain]

@treeder seems like need to contact them first

1. The doc is outdated (some files from link above one are absent and the doc is ~1 year old)
2. Check this discussion - https://github.com/MetaMask/metamask-extension/pull/2815 seems like they just added ability to use any custom endpoint and that's all, and also this discussion - https://github.com/MetaMask/metamask-extension/issues/3604
3. I also checked the code and found that custom URLs are not supported at all (ie - https://github.com/MetaMask/metamask-extension/blob/develop/old-ui/lib/etherscan-prefix-for-network.js those are prefixes for .infura.io - all endpoints are on this domain)

@treeder thoughts?

[treeder]

So sounds like they aren't open to it yet huh? Guess we'll have to wait.