add docs to show zkApp devs how to detect and present choice of wallets to users

[barriebyron]

The Implement ZkApp transaction of the MinaPortal Wiki page contains starter content

Resources and links Also https://github.com/sotatek-dev/mina-wallet-selector (not sure if it’s a good implementation but these are the sorts of thing you need for e2e zkApp flows)

https://snaps.metamask.io/snap/npm/mina-portal/

https://chrome.google.com/webstore/detail/metamask-flask-developmen/ljfoeinjpaedjfecbmggjgodbgkmjkjk

[barriebyron]

open PR https://github.com/sotatek-dev/mina-snap/pull/226/files#diff-342965aca989dae2e06ca2c8c8504869d84d87163ab75596e6ec8e8c5ffbf950R76 with request for input from team