Add/update DCO, CoC, contributing ... files (#93)

## Description

Update non code files to be uniformish amongst all repos.

## Why is this needed

Ensures our repos are all licensed correctly and contain similar/minimum
contribution info files.

Author: mergify[bot]

CONTRIBUTING.md

@@ -0,0 +1,45 @@
+## Hello Contributors!
+
+Thanks for your interest!
+We're so glad you're here.
+
+### Important Resources
+
+#### bugs: [https://github.com/tinkerbell/sandbox/issues](https://github.com/tinkerbell/sandbox/issues)
+
+### Code of Conduct
+
+Please read and understand the code of conduct found [here](https://github.com/tinkerbell/.github/blob/master/CODE_OF_CONDUCT.md).
+
+### DCO Sign Off
+
+Please read and understand the DCO found [here](docs/DCO.md).
+
+### Environment Details
+
+Building is handled by `make`, please see the [Makefile](Makefile) for available targets.
+
+#### Nix
+
+This repo's build environment can be reproduced using `nix`.
+
+##### Install Nix
+
+Follow the [Nix installation](https://nixos.org/download.html) guide to setup Nix on your box.
+
+##### Load Dependencies
+
+Loading build dependencies is as simple as running `nix-shell` or using [lorri](https://github.com/nix-community/lorri).
+If you have `direnv` installed the included `.envrc` will make that step automatic.
+
+### How to Submit Change Requests
+
+Please submit change requests and / or features via [Issues](https://github.com/tinkerbell/sandbox/issues).
+There's no guarantee it'll be changed, but you never know until you try.
+We'll try to add comments as soon as possible, though.
+
+### How to Report a Bug
+
+Bugs are problems in code, in the functionality of an application or in its UI design; you can submit them through [Issues](https://github.com/tinkerbell/sandbox/issues).
+
+## Code Style Guides

docs/DCO.md

@@ -0,0 +1,62 @@
+# DCO Sign Off
+
+All authors to the project retain copyright to their work. However, to ensure
+that they are only submitting work that they have rights to, we are requiring
+everyone to acknowledge this by signing their work.
+
+Since this signature indicates your rights to the contribution and
+certifies the statements below, it must contain your real name and
+email address. Various forms of noreply email address must not be used.
+
+Any copyright notices in this repository should specify the authors as "The
+project authors".
+
+To sign your work, just add a line like this at the end of your commit message:
+
+```text
+Signed-off-by: Jess Owens <[email protected]>
+```
+
+This can easily be done with the `--signoff` option to `git commit`.
+
+By doing this you state that you can certify the following (from [https://developercertificate.org/][1]):
+
+```text
+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+1 Letterman Drive
+Suite D4700
+San Francisco, CA, 94129
+
+Everyone is permitted to copy and distribute verbatim copies of this
+license document, but changing it is not allowed.
+
+
+Developer's Certificate of Origin 1.1
+
+By making a contribution to this project, I certify that:
+
+(a) The contribution was created in whole or in part by me and I
+    have the right to submit it under the open source license
+    indicated in the file; or
+
+(b) The contribution is based upon previous work that, to the best
+    of my knowledge, is covered under an appropriate open source
+    license and I have the right under that license to submit that
+    work with modifications, whether created in whole or in part
+    by me, under the same open source license (unless I am
+    permitted to submit under a different license), as indicated
+    in the file; or
+
+(c) The contribution was provided directly to me by some other
+    person who certified (a), (b) or (c) and I have not modified
+    it.
+
+(d) I understand and agree that this project and the contribution
+    are public and that a record of the contribution (including all
+    personal information I submit with it, including my sign-off) is
+    maintained indefinitely and may be redistributed consistent with
+    this project or the open source license(s) involved.
+```