refine READMEs for the subpackages

[wangchao1230]

Description

Please add an informative description that covers that changes made by the pull request and link all relevant issues.

All Promptflow Contribution checklist:

• The pull request does not introduce [breaking changes].
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.
• Create an issue and link to the pull request to get dedicated review from promptflow team. Learn more: suggested workflow.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[github-actions]

promptflow-tracing test result

 12 files   12 suites   4m 4s ⏱️
  9 tests   9 ✅ 0 💤 0 ❌
108 runs  108 ✅ 0 💤 0 ❌

Results for commit 32f7918.

♻️ This comment has been updated with latest results.

[github-actions]

SDK CLI Global Config Test Result clwan/layering_sdk_readme

3 tests   3 ✅  46s ⏱️
1 suites  0 💤
1 files    0 ❌

Results for commit 32f7918.

♻️ This comment has been updated with latest results.

[github-actions]

promptflow SDK CLI Azure E2E Test Result clwan/layering_sdk_readme

  4 files    4 suites   4m 2s ⏱️
201 tests 181 ✅ 20 💤 0 ❌
804 runs  724 ✅ 80 💤 0 ❌

Results for commit 32f7918.

♻️ This comment has been updated with latest results.

[github-actions]

Executor Unit Test Result clwan/layering_sdk_readme

754 tests   754 ✅  3m 45s ⏱️
  1 suites    0 💤
  1 files      0 ❌

Results for commit 32f7918.

[github-actions]

Executor E2E Test Result clwan/layering_sdk_readme

223 tests   221 ✅  6m 22s ⏱️
  1 suites    2 💤
  1 files      0 ❌

Results for commit 32f7918.

[github-actions]

SDK CLI Test Result clwan/layering_sdk_readme

   12 files     12 suites   48m 32s ⏱️
  513 tests   494 ✅ 19 💤 0 ❌
2 052 runs  1 976 ✅ 76 💤 0 ❌

Results for commit 32f7918.