(chore) improve AATH readme with some dev instructions #7724

Job	Run time
workspace_clippy (vdrtools_wallet)	3m 32s
workflow-setup	19s
verify-code-formatting	25s
workspace_clippy (askar_wallet)	3m 47s
aries_vcx_clippy (credx,vdrtools_wallet)	2m 25s
aries_vcx_clippy (vdr_proxy_ledger,vdrtools_wallet)	2m 17s
test-wallet-migrator	54s
workflow-setup-check	1s
test-unit-workspace	2m 5s
build-docker-vdrproxy	5s
test-compatibility-aries-vcx-wallet	52s
build-docker-aath-backchannel	0s
test-integration-aries-vcx (vdrtools_wallet,credx)	6m 35s
test-integration-aries-vcx (askar_wallet,credx)	6m 42s
test-integration-aries-vcx-anoncreds-rs	3m 32s
test-integration-aries-vcx-mysql	2m 16s
test-integration-did-crate	1m 38s
publish-docker-aath-backchannel	0s
test-integration-aries-vcx-vdrproxy	11m 39s
publish-docker-vdrproxy	2s
make-release	0s
	49m 6s

Provide feedback