docs(weave): add redact_pii_exclude_fields setting

weave/guides/tracking/redact-pii.mdx

@@ -16,6 +16,7 @@ The Sensitive Data Protection feature introduces the following functionality to
 - A `redact_pii` setting, which can be toggled on or off in the `weave.init` call to enable PII redaction.
 - Automatic redaction of [common entities](#entities-redacted-by-default) when `redact_pii = True`.
 - Customizable redaction fields using the configurable `redact_pii_fields` setting.
+- Exclude specific entities from redaction using the `redact_pii_exclude_fields` setting.
 
 ## Enable PII redaction
 
@@ -43,6 +44,14 @@ To get started with the Sensitive Data Protection feature in Weave, complete the
 
     For a full list of the entities that can be detected and redacted, see [PII entities supported by Presidio](https://microsoft.github.io/presidio/supported_entities/).
 
+4. (Optional) Exclude specific entities from redaction using the `redact_pii_exclude_fields` parameter. This is useful when you want to keep the default redaction but preserve certain entity types:
+
+    ```python lines
+    weave.init("my-project", settings={"redact_pii": True, "redact_pii_exclude_fields":["EMAIL_ADDRESS", "PERSON"]})
+    ```
+
+    In this example, all [default entities](#entities-redacted-by-default) are redacted except for `EMAIL_ADDRESS` and `PERSON`.
+
 ## Entities redacted by default
 
 The following entities are automatically redacted when PII redaction is enabled: