docs: update anomaly detector docs

[JessicaXYWang]

Related Issues/PRs

#xxx

What changes are proposed in this pull request?

Briefly describe the changes included in this Pull Request.

How is this patch tested?

• I have written tests (not required for typo or doc fix) and confirmed the proposed feature/bug-fix/change works.

Does this PR change any dependencies?

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• Yes. Make sure the dependencies are resolved correctly, and list changes here.

Does this PR add a new feature? If so, have you added samples on website?

• No. You can skip this section.
• Yes. Make sure you have added samples following below steps.

1. Find the corresponding markdown file for your new feature in website/docs/documentation folder.
   Make sure you choose the correct class estimators/transformers and namespace.
2. Follow the pattern in markdown file and add another section for your new API, including pyspark, scala (and .NET potentially) samples.
3. Make sure the DocTable points to correct API link.
4. Navigate to website folder, and run yarn run start to make sure the website renders correctly.
5. Don't forget to add <!--pytest-codeblocks:cont--> before each python code blocks to enable auto-tests for python samples.
6. Make sure the WebsiteSamplesTests job pass in the pipeline.

[github-actions]

Hey @JessicaXYWang 👋!
Thank you so much for contributing to our repository 🙌.
Someone from SynapseML Team will be reviewing this pull request soon.

We use semantic commit messages to streamline the release process.
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• fix: Fix LightGBM crashes with empty partitions
• feat: Make HTTP on Spark back-offs configurable
• docs: Update Spark Serving usage
• build: Add codecov support
• perf: improve LightGBM memory usage
• refactor: make python code generation rely on classes
• style: Remove nulls from CNTKModel
• test: Add test coverage for CNTKModel

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[JessicaXYWang]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov-commenter]

Codecov Report

Merging #2103 (d264478) into master (cd43ee7) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2103      +/-   ##
==========================================
- Coverage   86.33%   86.30%   -0.03%     
==========================================
  Files         312      312              
  Lines       16292    16292              
  Branches      832      832              
==========================================
- Hits        14065    14061       -4     
- Misses       2227     2231       +4     

see 4 files with indirect coverage changes

[mhamilton723]

Left some suggestions on the writing

[JessicaXYWang]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).