changelog: more review fixes/release/v0.31.0 (#3427)

* Update release summary

* Add pubsub config changes

* Add link to issue for pubsub changes

CHANGELOG.md

@@ -7,10 +7,19 @@
 Special thanks to external contributors on this release:
 @danil-lashin, @guagualvcha, @jleni, @siburu, @silasdavis, @srmo, @Stumble, @svenstaro 
 
+This release brings pubsub 2.0, limits the mempool size to 1GB (max_txs_bytes) and number of `/subscribe` WebSocket 
+clients (`max_subscription_clients`) and adds `/unsubscribe_all` endpoint to the lite client. 
+It also contains many smaller improvements and bug-fixes. 
+Pubsub 2.0 is an improved version of the older pubsub, which is a) non-blocking b) has nicer API. 
+Note our HttpClient's interface got updated to reflect the pubsub changes and now also has a better API for WebSocket subscriptions.
+
 ### BREAKING CHANGES:
 
 * CLI/RPC/Config
 - [rpc/client] Update Subscribe interface to reflect new pubsub/eventBus API [ADR-33](https://github.com/tendermint/tendermint/blob/develop/docs/architecture/adr-033-pubsub.md)
+- [config] [\#2826](https://github.com/tendermint/tendermint/issues/2826) Add `rpc.max_subscription_clients` config parameter to control how many unique clientIDs can `/subscribe` at the same time
+- [config] [\#2826](https://github.com/tendermint/tendermint/issues/2826) Add `rpc.max_subscriptions_per_client` config parameter to control how many unique queries a given client can `/subscribe` to
+- [config] [\#2826](https://github.com/tendermint/tendermint/issues/2826) Add `rpc.max_subscription_clients` config parameter allowing you to change time to wait for a tx to be committed during `/broadcast_tx_commit`
 
 * Apps