doc: improve `stream.Writable` ctor encoding option docs
- Document
defaultEncoding
. This was previously undocumented. - Clarify
decodeStrings
. In particular, the previous description was talking about decoding, which matches the unfortunate option name, but what actually happens is usually refererred to as encoding a string into a binary form.
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
documentation is changed or added -
commit message follows commit guidelines