[repo docs][github wiki][readme] Standardize documentation

[tapaswenipathak]

This looks nearly apt:

Still see for:

1. [android-client][ github wiki] Standardize Documentation android-client#1876
2. [github wiki][reduce entry points/dups] Standardize Documentation mobile-wallet#1331

Redirect to developer documentation:

1. delete/archive: https://docs.google.com/document/d/1oXQ2mNojyDFkY_x4RBRPaqS-xhpnDE9coQnbmI3Pobw/edit#heading=h.vhgp8hu9moqn

cc @edcable.