chore(docs): readme.md and contributing doc updates

[tabgok]

This commit contains two small changes to documentation:

1. Adds a WARNING message for installing git pre-commit hooks and instructions on how to uninstall.
2. Updates the link to the integration checklist template in the contributing to integrations document

Testing Strategy: N/A
Risks: None

Checklist

• Change(s) are motivated and described in the PR description.
• Testing strategy is described if automated tests are not included in the PR.
• Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• Change is maintainable (easy to change, telemetry, documentation).
• Library release note guidelines are followed.
• Documentation is included (in-code, generated user docs, public corp docs).
• Author is aware of the performance implications of this PR as reported in the benchmarks PR comment.

Reviewer Checklist

• Title is accurate.
• No unnecessary changes are introduced.
• Description motivates each change.
• Avoids breaking API changes unless absolutely necessary.
• Testing strategy adequately addresses listed risk(s).
• Change is maintainable (easy to change, telemetry, documentation).
• Release note makes sense to a user of the library.
• Reviewer is aware of, and discussed the performance implications of this PR as reported in the benchmarks PR comment.

[pr-commenter]

Benchmarks

Comparing candidate commit bea7ece in PR branch teague.bick-update-readme-githooks with baseline commit 883f685 in branch 1.x.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 56 cases.

[codecov-commenter]

Codecov Report

Merging #5426 (91356bf) into 1.x (35ab4b7) will decrease coverage by 0.04%.
The diff coverage is 72.39%.

@@            Coverage Diff             @@
##              1.x    #5426      +/-   ##
==========================================
- Coverage   76.66%   76.62%   -0.04%     
==========================================
  Files         909      910       +1     
  Lines       71308    71563     +255     
==========================================
+ Hits        54667    54836     +169     
- Misses      16641    16727      +86     

Impacted Files	Coverage Δ
ddtrace/internal/constants.py	0.00% <0.00%> (ø)
ddtrace/internal/encoding.py	46.91% <ø> (ø)
tests/appsec/iast/test_weak_hash.py	100.00% <ø> (ø)
tests/utils.py	90.27% <ø> (-0.24%)	⬇️
tests/tracer/test_writer.py	96.85% <20.00%> (-2.90%)	⬇️
tests/tracer/test_span.py	97.36% <33.33%> (-1.29%)	⬇️
ddtrace/contrib/aws_lambda/patch.py	78.33% <45.45%> (-6.86%)	⬇️
ddtrace/appsec/iast/taint_sinks/sql_injection.py	78.57% <50.00%> (-21.43%)	⬇️
ddtrace/contrib/aiohttp/patch.py	92.68% <50.00%> (-1.07%)	⬇️
ddtrace/internal/processor/trace.py	58.08% <50.00%> (-0.38%)	⬇️
... and 20 more

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[emmettbutler]

@tabgok adding the changelog/no-changelog label to this PR will make the "validate changelog" CI step pass.

[majorgreys]

Can we open a bug report for this?

[Yun-Kim]

Hi @tabgok, I've squashed your commits and signed them so that we can merge. Thanks for your contribution!