Document how to apply the wrapper in code

[tianchu]

What does this PR do?

Document how to apply the wrapper in code

Motivation

We have encountered a few cases (very rare though) where people have good reasons not being able to redirect the handler, but must apply the wrapper in code. Let's document it.

Testing Guidelines

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)

[codecov-commenter]

Codecov Report

Merging #246 (53ac038) into main (86bf652) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #246   +/-   ##
=======================================
  Coverage   83.52%   83.52%           
=======================================
  Files          35       35           
  Lines        1335     1335           
  Branches      283      283           
=======================================
  Hits         1115     1115           
  Misses        196      196           
  Partials       24       24           

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