Add link to fpdf2 + .id on headings in maintainer-guidelines.md

[Lucas-C]

I used a small JS <script> that I have been using for a while in order to create "linkable" headings on this page,
in order for the table of content to work: https://py-pdf.github.io/pages/maintainer-guidelines.html

[Lucas-C]

@MartinThoma: I disabled the Require signed commits setting on this repository in order to merge this PR.

The issue that I have is that:

• I use an anonymized git user.email for my commits (which BTW is required by the repo / org settings), provided by GitHub: 925560+Lucas-C@users.noreply.github.com
• my GPG key does not include this anonymized GitHub email address, only my own my personal address. This leads to my commits being signed, but GitHub considering them to be "Unverified", as the signature does not match the commit author email address

The only "clean" solution would be for me to re-generate a new GPG signing key that includes my Gitlab & GitHub anonymized email address, but I won't undertake this task now.

Is this OK with you or do you really wish for all commits to be signed on this repository?

[Lucas-C]

By the way, how is the website published? https://py-pdf.github.io/

This does not seem automated through GitHub Actions when new commits land on the main branch:
https://github.com/py-pdf/py-pdf.github.io/actions