fix(doc): doc under stream crate

[lmatz]

What's changed and what's your intention?

PLEASE DO NOT LEAVE THIS EMPTY !!!
As the title.

Refer to a related PR or issue link (optional)

#1437

[codecov]

Codecov Report

Merging #1461 (7c1af34) into main (8a40888) will increase coverage by 0.04%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main    #1461      +/-   ##
============================================
+ Coverage     70.17%   70.21%   +0.04%     
  Complexity     2766     2766              
============================================
  Files          1028     1028              
  Lines         90065    90139      +74     
  Branches       1790     1790              
============================================
+ Hits          63201    63294      +93     
+ Misses        25973    25954      -19     
  Partials        891      891              

Flag	Coverage Δ
java	61.01% <ø> (ø)
rust	72.18% <ø> (+0.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
rust/stream/src/executor/aggregation/agg_call.rs	87.50% <ø> (ø)
...st/stream/src/executor/aggregation/agg_executor.rs	91.11% <ø> (ø)
rust/stream/src/executor/batch_query.rs	55.22% <ø> (ø)
rust/stream/src/executor/mview/state.rs	100.00% <ø> (ø)
rust/stream/src/task/mod.rs	54.32% <ø> (ø)
rust/meta/src/stream/graph/stream_graph.rs	58.26% <0.00%> (-1.98%)	⬇️
rust/storage/src/hummock/test_utils.rs	80.48% <0.00%> (-0.24%)	⬇️
rust/storage/src/hummock/error.rs	13.46% <0.00%> (ø)
rust/storage/src/hummock/sstable_store.rs	86.60% <0.00%> (ø)
rust/bench/ss_bench/main.rs	0.98% <0.00%> (+0.01%)	⬆️
... and 5 more

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