Consider adding a listing of installed syspatches

[morgant]

I just noticed that syspatch notes that errata for installed syspatches can be found in /var/syspatch for OpenBSD -stable. For example, on OpenBSD amd64/7.5-stable as of 2024-08-01, I have the following directories:

/var/syspatch/75-001_xserver/
/var/syspatch/75-003_libcrypto/
/var/syspatch/75-004_bgpd/
/var/syspatch/75-005_sndiod/

And within each, there are *.patch.sig & rollback.tgz files. For example, in /var/syspatch/75-005_sndiod, there are:

/var/syspatch/75-005_sndiod/005_sndiod.patch.sig
/var/syspatch/75-005_sndiod/rollback.tgz

And ???_*.patch.sig contains the errata, instructions on how to build & apply the patch, and the source code diff.

This could be useful for listing already installed patches and listing the *.patch.sig files for the user to glean more information, plus a link to the errata page.