[DOCS] clarify logger format handling (#4149)

Author: SyedAsadRazaDevops

api/include/opentelemetry/logs/logger.h

@@ -430,8 +430,11 @@ class Logger
    *
    * @param severity severity of the log
    * @param event_id event identifier of the log
-   * @param format an utf-8 string following https://messagetemplates.org/
+   * @param format a UTF-8 string stored as the log record body
    * @param attributes key value pairs of the log
+   *
+   * @note The @p format string is not interpolated with values from
+   *       @p attributes. Pass structured data through @p attributes.
    */
   virtual void Log(Severity severity,
                    const EventId &event_id,