Fix a link rot.
RELNOTES: None
@@ -291,7 +291,7 @@ For each [label attribute](lib/attr.html#label), you can decide whether the
dependency should be built in the same configuration, or transition to the host
configuration (using `cfg`). If a label attribute has the flag
`executable=True`, the configuration must be set explicitly.
-[See example](cookbook.html#execute-a-binary)
+[See example](cookbook.md#execute-a-binary)
In general, sources, dependent libraries, and executables that will be needed at
runtime can use the same configuration.
