docs: add Jenkins CSP troubleshooting for blank static reports

[Hashim1999164]

Summary

• Adds a Troubleshooting section for blank static reports when viewed in Jenkins.
• Explains that Jenkins sandboxed iframes block scripts needed by the report.
• Points to the CSP workaround discussion in Add troubleshooting documentation for: Cannot display report in Jenkins due to sandboxed iframe #168.

Fixes #168

Test plan

• Confirm the new Troubleshooting subsection appears under the existing one in README.md
• Confirm the link to Add troubleshooting documentation for: Cannot display report in Jenkins due to sandboxed iframe #168#issuecomment-381748354 opens correctly

[linux-foundation-easycla]

• ❌ - login: @Hashim1999164 / name: Hashim Khan. The commit (5996b70) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.

[changeset-bot]

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[alexander-akait]

Please accept CLA