Update docs relating to the multiple notary support work

docs/source/release-notes.rst

@@ -8,6 +8,20 @@ Unreleased
 
 Here are changes in git master that haven't yet made it to a snapshot release:
 
+* Made the ``NotaryService`` extensible, we now have both validating and non-validating notaries.
+* Added a protocol for changing the notary for a state.
+* Every ``ContractState`` now has to specify a *participants* field, which is a list of parties that are able to
+  consume this state in a valid transaction. This is used for e.g. making sure all relevant parties obtain the updated
+  state when changing a notary.
+* Introduced ``TransactionState``, which wraps ``ContractState``, and is used when defining a transaction output.
+  The notary field is moved from ``ContractState`` into ``TransactionState``.
+* Every transaction now has a *type* field, which specifies custom build & validation rules for that transaction type.
+  Currently two types are supported:
+
+  - **General**. Runs the default build and validation logic.
+  - **NotaryChange**. Contract code is not run during validation, checks that the notary field is the only difference
+    between the inputs and outputs.
+
 * The cash contract has moved from com.r3corda.contracts to com.r3corda.contracts.cash.
 * Amount class is now generic, to support non-currency types (such as assets, or currency with additional information).
 * Refactored the Cash contract to have a new FungibleAsset superclass, to model all countable assets that can be merged