Markdown produces invalid results

[Christopher Yeleighton]

When I unzip /usr/share/doc/docker.io/README.md.gz and process it through markdown, I get an invalid document, including:

Line 1, Column 1: no document type declaration; will parse without validation

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: markdown 1.0.1-7
ProcVersionSignature: Ubuntu 3.19.0-30.33~14.04.1-generic 3.19.8-ckt6
Uname: Linux 3.19.0-30-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.15
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Oct 9 14:04:54 2015
InstallationDate: Installed on 2014-08-20 (414 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=pl
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=pl_PL.UTF-8
 SHELL=/bin/bash
SourcePackage: markdown
UpgradeStatus: No upgrade log present (probably fresh install)