Add release notes for #6122 (`asOfHeight` RPC parameters).

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

doc/release-notes.md

@@ -15,3 +15,31 @@ Memory Usage Improvement
 
 The memory usage of zcashd has been reduced by not keeping Equihash solutions for all
 block headers in memory.
+
+RPC changes
+-----------
+
+The following RPC methods that query wallet state now support an optional `asOfHeight`
+parameter, to execute the query as if it were run when the blockchain was at the height
+specified by this argument:
+
+* `getbalance`
+* `getreceivedbyaddress`
+* `gettransaction` (*)
+* `getwalletinfo`
+* `listaddressgroupings`
+* `listreceivedbyaddress` (*)
+* `listsinceblock` (*)
+* `listtransactions`
+* `listunspent` (*)
+* `z_getbalanceforaccount`
+* `z_getbalanceforviewingkey`
+* `z_getmigrationstatus`
+* `z_getnotescount` (also adds `minconf` parameter)
+* `z_listreceivedbyaddress`
+* `z_listunspent`
+
+(*) For these methods, additional parameters have been added to maintain
+compatibility of parameter lists with Bitcoin Core. Default values should be
+passed for these additional parameters in order to use `asOfHeight`. See the
+[RPC documentation](https://zcash.github.io/) for details.