Document pallets in readme (nodes/rust/duniter-v2s!122)

* improve authority doc

* more doc

* update onshot accounts readme

* doc xtask

* doc runtime

* doc todo

* doc todo

* doc pallets

* doc todo

* doc ud

* doc oneshot

* doc authority members

* doc certification

* doc wot

* doc membership

* doc identity

* fix typo

* doc duniter-account