community: update contributing guide (envoyproxy#139)

Fixes envoyproxy#138

Signed-off-by: Matt Klein <mklein@lyft.com>
Signed-off-by: Diego Erdody <diego@medallia.com>

CODE_OF_CONDUCT.md

@@ -1 +1,3 @@
-This project is governed by [Lyft's code of conduct](https://github.com/lyft/code-of-conduct). All contributors and participants agree to abide by its terms.
+## Community Code of Conduct
+
+ratelimit follows the [CNCF Code of Conduct](https://github.com/cncf/foundation/blob/master/code-of-conduct.md).

CONTRIBUTING.md

@@ -8,12 +8,85 @@ We welcome contributions from the community. Here are some guidelines.
 
 * Fork the repo and create your PR.
 * Tests will automatically run for you.
-* When all of the tests are passing, tag @lyft/network-team and we will review it and
-  merge once our CLA has been signed (see below).
+* When all of the tests are passing, tag @envoyproxy/ratelimit-maintainers and
+  we will review it and merge.
 * Party time.
 
-# CLA
+# DCO: Sign your work
 
-* We require a CLA for code contributions, so before we can accept a pull request we need
-  to have a signed CLA. Please visit our [CLA service](https://oss.lyft.com/cla) and follow
-  the instructions to sign the CLA.
+The sign-off is a simple line at the end of the explanation for the
+patch, which certifies that you wrote it or otherwise have the right to
+pass it on as an open-source patch. The rules are pretty simple: if you
+can certify the below (from
+[developercertificate.org](https://developercertificate.org/)):
+
+```
+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+660 York Street, Suite 102,
+San Francisco, CA 94110 USA
+
+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.
+```
+
+then you just add a line to every git commit message:
+
+    Signed-off-by: Joe Smith <joe@gmail.com>
+
+using your real name (sorry, no pseudonyms or anonymous contributions.)
+
+You can add the sign off when creating the git commit via `git commit -s`.
+
+If you want this to be automatic you can set up some aliases:
+
+```bash
+git config --add alias.amend "commit -s --amend"
+git config --add alias.c "commit -s"
+```
+
+## Fixing DCO
+
+If your PR fails the DCO check, it's necessary to fix the entire commit history in the PR. Best
+practice is to [squash](https://gitready.com/advanced/2009/02/10/squashing-commits-with-rebase.html)
+the commit history to a single commit, append the DCO sign-off as described above, and [force
+push](https://git-scm.com/docs/git-push#git-push---force). For example, if you have 2 commits in
+your history:
+
+```bash
+git rebase -i HEAD^^
+(interactive squash + DCO append)
+git push origin -f
+```
+
+Note, that in general rewriting history in this way is a hindrance to the review process and this
+should only be done to correct a DCO mistake.

DCO

@@ -0,0 +1,37 @@
+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.