Update Falco README

[domalessi]

What does this PR do?

https://datadoghq.atlassian.net/browse/DOCS-11418

Feedback:

When viewing the Falco Integration documentation, changing the site from the side panel does not update the intake URL. The intake should change based on the site, for EU should be:https://http-intake.logs.datadoghq.eu/api/v2/logs?dd-api-key=&ddsource=falco.

The exact functionality requested is not supported in integrations-core, so I went with a workaround. This PR replaces the specific URLs with placeholders and adds a note to clarity that the the placeholder must be updated according to your DD site.

Motivation

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[aliciascott]

looks good!

Review from aliciascott is dismissed. Related teams and files:

• documentation
  • falco/README.md

Review from steveny91 is dismissed. Related teams and files:

• agent-integrations
  • falco/README.md