[Rules] Add section on non-ASCII header values (cloudflare#17605)

Author: pedrosousa

src/content/docs/rules/transform/managed-transforms/reference.mdx

@@ -76,6 +76,12 @@ Adds HTTP headers with location information for the visitor's IP address to the
 Turning on [IP geolocation](/network/ip-geolocation/) will send a `cf-ipcountry` HTTP header to your origin server even when **Add visitor location headers** is turned off.
 :::
 
+#### Encoding of non-ASCII header values
+
+Cloudflare always converts non-ASCII characters to UTF-8 (using hexadecimal character representation) in HTTP request and response header values. This applies to location headers added by the **Add visitor location headers** managed transform.
+
+For example, the header value `São Paulo` would be encoded as `S\u00c3\u00a3o Paulo`.
+
 ### Add "True-Client-IP" header
 
 :::note