Update DevelopmentGuide

[sarahchen6]

What does this PR do?
Updates the DevelopmentGuide with a JRuby example and a few other minor fixes.

Motivation:
I was a bit confused when trying to test JRuby versions and thought I'd go through the DevelopmentGuide while I was at it.

Change log entry
No

Additional Notes:

How to test the change?
Check that everything reads well.

[datadog-official]

⚠️ Tests

⚠️ Warnings

❄️ 1 New flaky test detected

Rails Rack with a soft controller error traces without explicit exception information from rspec (Datadog) (✨ Fix with BitsAI)

server closed the connection unexpectedly
	This probably means the server terminated abnormally
	before or while processing the request.

Failure/Error: initialize!

PG::UnableToSend:
  server closed the connection unexpectedly
  	This probably means the server terminated abnormally
  	before or while processing the request.
...

ℹ️ Info

🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 100.00%
• Total Coverage: 101.96% (-0.02%)

View detailed report

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 14c7788 | Docs | Was this helpful? Give us feedback!}

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-10-03 21:09:52

Comparing candidate commit 14c7788 in PR branch sarahchen/test-doc-update with baseline commit eae7fc6 in branch master.

Found 3 performance improvements and 1 performance regressions! Performance is the same for 40 metrics, 2 unstable metrics.

scenario:error - error tracking, with_error=true - all

• 🟩 throughput [+358.972op/s; +381.631op/s] or [+5.313%; +5.649%]

scenario:error - error tracking, with_error=true - user code only

• 🟩 throughput [+392.955op/s; +413.729op/s] or [+5.887%; +6.198%]

scenario:profiling - intern_all 1000 repeated strings

• 🟩 throughput [+6951.920op/s; +7011.649op/s] or [+40.917%; +41.269%]

scenario:tracing - Tracing.log_correlation

• 🟥 throughput [-10460.524op/s; -10134.817op/s] or [-9.493%; -9.197%]

[ivoanjo]

👍 LGTM thanks for improving the docs!