Added note about hiredis to the RELEASE notes.
MODIFY
RELEASE_NOTES.md
RELEASE_NOTES.md
## Version 3.5.5
* Support Redis version 5.x.
+* If you want to use a `redis-rb` gem version after 5.0.0, you must
+ add the `hiredis-client` gem to your application Gemfile.
* Support setting Redis timeouts in the Beetle configuration. Default
is 5.0 seconds for all timeouts as this is the default for redis gem
versions before 5.0.0.

Added note about hiredis to the RELEASE notes.