types/logger: add more reserved top level field names
@@ -56,8 +56,8 @@ type jenc struct {
// JSON object that is logged. That is, if recType is "foo" and v is
// 123, the value logged is {"foo":123}.
//
-// Do not use recType "logtail" or "v", with any case. Those are
-// reserved for the logging system.
+// Do not use recType "logtail", "v", "text", or "metrics", with any case.
+// Those are reserved for the logging system.
//
// The level can be from 0 to 9. Levels from 1 to 9 are included in
// the logged JSON object, like {"foo":123,"v":2}.
