[ISSUE #563] Optimize example and doc for Rust SDK

[ShadowySpirits]

close #563

[codecov-commenter]

Codecov Report

Merging #564 (1b51834) into master (7fa131f) will increase coverage by 12.09%.
The diff coverage is 44.44%.

@@              Coverage Diff              @@
##             master     #564       +/-   ##
=============================================
+ Coverage     34.74%   46.84%   +12.09%     
  Complexity      667      667               
=============================================
  Files           195      208       +13     
  Lines          8851    11889     +3038     
  Branches        281     3319     +3038     
=============================================
+ Hits           3075     5569     +2494     
- Misses         5618     6075      +457     
- Partials        158      245       +87     

Flag	Coverage Δ
rust	81.99% <44.44%> (?)

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Impacted Files	Coverage Δ
rust/src/model/transaction.rs	82.29% <ø> (ø)
rust/src/client.rs	82.30% <27.27%> (ø)
rust/src/simple_consumer.rs	85.79% <50.00%> (ø)
rust/src/producer.rs	91.80% <57.14%> (ø)

... and 10 files with indirect coverage changes

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[lizhanhui]

OK