📝 [RUM-5172] add react integration documentation

[BenoitZugmeyer]

Motivation

Document how to use the react integration. See it rendered: https://github.com/DataDog/browser-sdk/blob/benoit/react-doc/packages/rum-react/README.md

Changes

Add documentation to the README

Testing

• Local
• Staging
• Unit
• End to end

---

I have gone over the contributing documentation.

[cit-pr-commenter]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	161.62 KiB	161.62 KiB	0 B	0.00%	✅
Logs	57.95 KiB	57.95 KiB	0 B	0.00%	✅
Rum Slim	110.14 KiB	110.14 KiB	0 B	0.00%	✅
Worker	25.21 KiB	25.21 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base Average Cpu Time (ms)	Local Average Cpu Time (ms)	𝚫
addglobalcontext	0.001	0.001	0.000
addaction	0.030	0.033	0.003
adderror	0.031	0.037	0.006
addtiming	0.001	0.001	0.000
startview	0.913	1.162	0.248
startstopsessionreplayrecording	0.780	1.027	0.247
logmessage	0.019	0.021	0.002

🧠 Memory Performance

Action Name	Base Consumption Memory (bytes)	Local Consumption Memory (bytes)	𝚫 (bytes)
addglobalcontext	20.46 KiB	19.79 KiB	-687 B
addaction	72.73 KiB	71.82 KiB	-931 B
adderror	86.60 KiB	88.72 KiB	2.13 KiB
addtiming	19.47 KiB	18.78 KiB	-703 B
startview	349.22 KiB	352.59 KiB	3.37 KiB
startstopsessionreplayrecording	14.21 KiB	14.34 KiB	125 B
logmessage	70.55 KiB	70.39 KiB	-161 B

🔗 RealWorld

[jhgilbert]

I left some comments for style. Let me know when you'd like another look. Thank you!

[datadog-datadog-prod-us1]

Library Vulnerabilities

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.67%. Comparing base (2490414) to head (a919bf4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2873      +/-   ##
==========================================
- Coverage   93.68%   93.67%   -0.02%     
==========================================
  Files         266      266              
  Lines        7584     7584              
  Branches     1687     1687              
==========================================
- Hits         7105     7104       -1     
- Misses        479      480       +1     

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