Add Developer Certificate of Origin Text

We purposely chose to license Docker under the Apache 2.0 license. This is a well-known
license, which is popular for its permissive and flexible properties, while still
encouraging a collaborative community. It also makes certain representations with regard
to contributions, and the rights given to contributors, the project, people who use Docker,
people who modify Docker, etc.

This approach to contributions is inspired by the popular Linux Developer
"Certificate of Origin". This approach makes it simple for new contributors to get started,
and avoids bureaucracy in tracking contributions and contributors.

To indicate accordance, each individual contribution to the Project is signed off by the
developer, using his or her real name, email address, and github handle in the format below:

	Docker-DCO-1.0-Signed-off-by: Joe Smith <joe.smith@email.com>
Merged with master
Return meaningful error for meaningless Dockerfiles
fix progressbar in docker push
 Installation for FrugalWare
+ added missing link in index.rst
* some gramatic and spelling fixes

Thx jamtur :)
add REMOTE_TODO
Remove old debug from tarsum
Make sure the cache lookup returns always the same result
Log files name along with their checksum in TarSum + add a Method to retrieve the checksum map
Change BuildFile in order to use TarSum instead of custom checksum
Hash the sums for directory (ureadable when there is too many
Exit with code 1 in case of error for `docker build`
* s/docker/Docker/
Fix typo in working with volumes doc page
Replace FPM --vendor with --license, and give it the proper value of "Apache-2.0"

Fixes #3372
Add DOCKER_HOST env var for client

This env var will set the -H flag on the docker
client.
Reorganize the syntax highlighting files in contrib under a common directory to match "contrib/init" and "contrib/completion"

This is split off from #2970.
add a simple note to suggest to the user to use RUN curl/wget/tool if the URL they need is behind auth
Make blank -H option default to the same as no -H was sent