doc: `readable.push()` supports `undefined` in non-object mode
I found that the readable stream that isn't in object mode supports undefined
long ago, and it's original idea is to express EOF. Now it is just treated as a empty string or buffer. But the doc and code aren't clear for it although it is not important.
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
documentation is changed or added -
commit message follows commit guidelines
Affected core subsystem(s)
doc, stream