Add explicit text for where an obindex call for generators was since obindex...

Add explicit text for where an obindex call for generators was since obindex does not cause output of its argument.

Doc/ref/ref3.tex

@@ -804,7 +804,8 @@ The following flag bits are defined for \member{co_flags}: bit
 to accept an arbitrary number of positional arguments; bit
 \code{0x08} is set if the function uses the \samp{**keywords} syntax
 to accept arbitrary keyword arguments; bit \code{0x20} is set if the
-function is a \obindex{generator}.
+function is a generator.
+\obindex{generator}
 
 Future feature declarations (\samp{from __future__ import division})
 also use bits in \member{co_flags} to indicate whether a code object