Runtime Documentation (#1282)

* add docs to parachain runtimes

* update and add top readme

* clarify docs

* review plus licenses

* Update parachains/README.md

* Update parachains/runtimes/assets/README.md

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* Update parachains/runtimes/assets/README.md

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

parachains/runtimes/assets/README.md

@@ -0,0 +1,25 @@
+# Assets Parachain
+
+Implementation of _Statemint_, a blockchain to support generic assets in the Polkadot and Kusama
+networks.
+
+Statemint allows users to:
+
+- Deploy promise-backed assets, both fungible and non-fungible, with a DOT/KSM deposit.
+- Set admin roles to manage assets and asset classes.
+- Register assets as "self-sufficient" if the Relay Chain agrees, i.e. gain the ability for an
+  asset to justify the existance of accounts sans DOT/KSM.
+- Pay transaction fees using sufficient assets.
+- Transfer (and approve transfer) assets.
+- Interact with the chain via its transactional API or XCM.
+
+Statemint must stay fully aligned with the Relay Chain it is connected to. As such, it will accept
+the Relay Chain's governance origins as its own.
+
+See
+[the article on Statemint as common good parachain](https://www.parity.io/blog/statemint-generic-assets-chain-proposing-a-common-good-parachain-to-polkadot-governance/)
+for a higher level description.
+
+Wallets, custodians, etc. should see
+[the Polkadot Wiki's Integration Guide](https://wiki.polkadot.network/docs/build-integrate-assets)
+for details about support.