[junaruga]

This PR fixes #1118.

The PR has 2 commits. The 1st commit enhances manual documents in html/OpenSSL/SSL/SSLContext.html, that are indirectly related to PQC, but not the PQC contents. The 2nd commit is the main commit adding the PQC documents in html/OpenSSL.html.

For the 2nd commit adds Post-Quantum Cryptography section with the 2 sub sections PQC Server and Client and Multiple Certificates (PQC and Classical) Server and Clients. I still believe the 2 cases are important. The case only allowing PQC-capable key exchange ML-KEM and signature ML-DSA, and the case allowing PQC-capable and classical key exchanges and signatures.

== Post-Quantum Cryptography
...
=== PQC Server and Client
...
=== Multiple Certificates (PQC and Classical) Server and Clients
...

For the content, I referred to SSL and TLS Connections section and aligned with it in html/OpenSSL/SSL/SSLContext.html for the example codes such as the variable names and loop do ... end. I tested all of added example codes by running Ruby scripts on my local. I also confirmed the generated rdoc documents.

If you would prefer a simpler document, and we have to remove one of the 2 sections, I would like to remove PQC Server and Client section, keeping Multiple Certificates (PQC and Classical) Server and Clients section.

Commit messages

The 1st commit

docs: Update OpenSSL::SSL::SSLContext#sigalgs= and #client_sigalgs=

Update the rdoc document for the following generated HTML file.

* html/OpenSSL/SSL/SSLContext.html

Assisted-by: Claude:Opus 4.6

The 2nd commit

docs: Add PQC (ML-KEM, ML-DSA) documentation

Add post-quantum cryptography documentation covering ML-KEM for key
exchange and ML-DSA for signature.

Update the rdoc document for the following generated HTML file.

* html/OpenSSL.html

Assisted-by: Claude:Opus 4.6

What do you think?