doc: add uv_metrics_idle_time() version metadata

Refs: https://github.com/libuv/libuv/pull/2725
PR-URL: https://github.com/libuv/libuv/pull/2984
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

docs/src/loop.rst

@@ -73,6 +73,8 @@ API
 
       This option is necessary to use :c:func:`uv_metrics_idle_time`.
 
+    .. versionchanged:: 1.39.0 added the UV_METRICS_IDLE_TIME option.
+
 .. c:function:: int uv_loop_close(uv_loop_t* loop)
 
     Releases all internal loop resources. Call this function only when the loop

docs/src/metrics.rst

@@ -23,3 +23,5 @@ API
         The event loop will not begin accumulating the event provider's idle
         time until calling :c:type:`uv_loop_configure` with
         :c:type:`UV_METRICS_IDLE_TIME`.
+
+    .. versionadded:: 1.39.0