debuginfod urls should be documented

[Christopher Yeleighton]

Since we do not enable debuginfod by default, it should be documented how to configure it, preferably in the file README.Debian.

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: gdb 12.1-0ubuntu1~22.04
ProcVersionSignature: Ubuntu 6.2.0-1016.16~22.04.1-azure 6.2.16
Uname: Linux 6.2.0-1016-azure x86_64
ApportVersion: 2.20.11-0ubuntu82.5
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Sun Nov 26 11:31:54 2023
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=pl_PL.UTF-8
 SHELL=/bin/bash
SourcePackage: gdb
UpgradeStatus: No upgrade log present (probably fresh install)