meth.log2 doc: add a link to int.bit_length()
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index d68cf11..62c0f34 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -191,6 +191,11 @@
 
    .. versionadded:: 3.3
 
+   .. seealso::
+
+      :meth:`int.bit_length` returns the number of bits necessary to represent
+      an integer in binary, excluding the sign and leading zeros.
+
 
 .. function:: log10(x)