Support SSL-enabled docker registry. Users need to set ENV_DOCKER_REGISTRY_USE_SSL
enable secure connection to Docker registry.
Add SSLProxyEngine instruction to apache config file.
Fix documentation
Add missing piece to Support SSL connection to Docker registry #8

These two options needed to be turned off in my case (see the pull request #8
for more information).

http://httpd.apache.org/docs/trunk/mod/mod_ssl.html#sslproxycheckpeername
http://httpd.apache.org/docs/trunk/mod/mod_ssl.html#sslproxycheckpeercn