doc: link to readable and writeable stream section

Modify the `[Writable]` and `[Readable]` links so they point
directly to the right sections in the stream.html doc

PR-URL: https://github.com/nodejs/node/pull/11517
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/process.md

@@ -1776,8 +1776,8 @@ cases:
 [Signal Events]: #process_signal_events
 [Stream compatibility]: stream.html#stream_compatibility_with_older_node_js_versions
 [TTY]: tty.html#tty_tty
-[Writable]: stream.html
-[Readable]: stream.html
+[Writable]: stream.html#stream_writable_streams
+[Readable]: stream.html#stream_readable_streams
 [Child Process]: child_process.html
 [Cluster]: cluster.html
 [`process.exitCode`]: #process_process_exitcode

doc/api/readline.md

@@ -525,8 +525,8 @@ rl.on('line', (line) => {
 
 [`process.stdin`]: process.html#process_process_stdin
 [`process.stdout`]: process.html#process_process_stdout
-[Writable]: stream.html
-[Readable]: stream.html
+[Writable]: stream.html#stream_writable_streams
+[Readable]: stream.html#stream_readable_streams
 [TTY]: tty.html
 [`SIGTSTP`]: readline.html#readline_event_sigtstp
 [`SIGCONT`]: readline.html#readline_event_sigcont