docs: add note on NATS jetstream beta package

[AlexCuse]

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 76.46%. Comparing base (57df621) to head (3a2fdd3). Report is 3 commits behind head on master.

:exclamation: Current head 3a2fdd3 differs from pull request most recent head 5c8f519

Please upload reports for the commit 5c8f519 to get more accurate results.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #405      +/-   ##
==========================================
+ Coverage   66.88%   76.46%   +9.57%     
==========================================
  Files          64       57       -7     
  Lines        4282     3012    -1270     
==========================================
- Hits         2864     2303     -561     
+ Misses       1242      569     -673     
+ Partials      176      140      -36     

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