Docs guardrails for what not to assert against

Minimal repro:

{
  "ci": {
    "assert": {
      "preset": "lighthouse:recommended",
      "assertions": {
        "critical-request-chains": ["warn", {"minScore": 1}]
      }
    }
}

This leads to:

  ⚠️  critical-request-chains warning for minScore assertion
     Minimize Critical Requests Depth
     Documentation: https://web.dev/critical-request-chains

        expected: >=1
           found: 0
      all values: 0, 0, 0

[patrickhulce]

We decided in person that we’ll just add some recipes for how to extend the presets

[patrickhulce]

ERROR: Asserting a minScore against an informative audit will never pass. Check you lighthouserc.

This isn’t true though. An informative audit will be marked notApplicable when it passes and your minScore assertion will pass as well.