update release notes

doc/relnotes/README.md

@@ -12,12 +12,24 @@ evil organizations.
 
 # Hush 3.9.1 ""
 
-This is an OPTIONAL release.
+This is an OPTIONAL release. It is most important for users with large wallets, as it fixes an important
+bug that causes the Hush full node to stop responding to requests.
 
+  * Fix RPC deadlocks, which caused the RPC interface to hang.
+    * A special thanks to ex-Hush developer miodrag who reported this in an upstream issue comment.
+    * This turned out to be an upstream bug in Zcash that was inherited by Hush.
+    * More details can be found at https://git.hush.is/hush/hush3/issues/77
   * The `listbanned` RPC now returns a new key `time_remaining` which tells how many
     seconds are remaining in the ban
   * The `rescan` RPC now works correctly when given a height. This can be used to do
     a partial rescan from a custom height, without restarting the node.
+  * Minimum disk space required for a running full node has been increased to 1GB from 50MB
+    * This will print "Disk space is low!!!" and shut down the full node.
+    * To fix, free up disk space and restart the node.
+    * This change was implemented because in rare circumstances, large amounts of disk space
+      can be used up quickly, faster than the node checks for free disk space, which can lead
+      to a corrupt wallet.dat . Requiring more free disk space makes this much less likely.
+  * Dockerfile has been updated
 
 # Hush 3.9.0 "Unusual Ursid"
 ```