vuxml: Document vulns in xorg-server and libX11

Document two vulnerabilities, one in xorg-server and one in libX11.
The one in libX11 is a heap corruption vulnerability. [1]
The one in xorg-server (and slave ports) is a uninitialized memory
disclosure. [2]

Security: CVE-2020-14344[1], CVE-2020-14347 [2]