fix link to instrumentation
diff --git a/Doc/whatsnew/3.6.rst b/Doc/whatsnew/3.6.rst
index 59ac332..e6d3973 100644
--- a/Doc/whatsnew/3.6.rst
+++ b/Doc/whatsnew/3.6.rst
@@ -423,7 +423,7 @@
 without the need to recompile specific debug builds or providing
 application-specific profiling/debugging code.
 
-More details in:ref:`instrumentation`.
+More details in :ref:`instrumentation`.
 
 The current implementation is tested on Linux and macOS.  Additional
 markers may be added in the future.