Revise integration app readme

[p-datadog]

What does this PR do?

Revises setup instructions in the integration app readme file to reflect issues I ran into trying to get the app going

Motivation:
Attempted to test the integration app

Change log entry
None

Additional Notes:

How to test the change?
N/A

[datadog-datadog-prod-us1]

Datadog Summary

✅ Code Quality    ✅ Code Security    ✅ Dependencies

Test Optimization Report

Branch report: integration-readme
Commit report: 3085ab5
Test service: dd-trace-rb

✅ 0 Failed, 21056 Passed, 1376 Skipped, 3m 44.96s Total Time

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.77%. Comparing base (7ce8685) to head (8bb2bb7).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4638      +/-   ##
==========================================
- Coverage   97.77%   97.77%   -0.01%     
==========================================
  Files        1415     1415              
  Lines       86561    86561              
  Branches     4386     4386              
==========================================
- Hits        84633    84631       -2     
- Misses       1928     1930       +2     

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[pr-commenter]

Benchmarks

Benchmark execution time: 2025-05-13 12:10:41

Comparing candidate commit 8bb2bb7 in PR branch integration-readme with baseline commit 7ce8685 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 31 metrics, 2 unstable metrics.