doc: make openssl maintenance position independent

It used to have some `cd` commands that if done literally would
invalidate the subsequent commands. Modify them to be more accurate,
which also simplifies pasting them directly into the console from the
guide while doing an update.

PR-URL: https://github.com/nodejs/node/pull/32977


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>