README.md: remove incorrect link to openssl.github.io

README.md: remove incorrect link to openssl.github.io

The link to the OpenSSL Project Pages <openssl.github.io>
actually points to an unfinished draft <mspncp.github.io>.

The original intention of this pet project of mine was to
have a website dedicated to describing the OpenSSL workflow
on GitHub and to answer frequently asked questions related
to pull requests and the review process.

The progress on that project has stalled and I'm not so sure
anymore whether it is good idea to have yet another project
website. In particular since the OpenSSL Wiki has seen some
revival and increased activity caused by the upcoming
OpenSSL 3.0 release.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/12361)