Update the CONTRIBUTING.md to follow the standard process.

CONTRIBUTING.md

@@ -1,8 +1,76 @@
 # Contributing to Mosaic
 
 ## Overview
-We happily welcome contributions to Mosaic. 
-We use GitHub Issues to track community reported issues and GitHub Pull Requests for accepting changes.
+We happily welcome contributions to Mosaic package. We use [GitHub Issues][https://github.com/databrickslabs/mosaic/issues] to track community reported issues and [GitHub Pull Requests][https://github.com/databrickslabs/mosaic/pulls] for accepting changes.
+Contributions are licensed on a license-in/license-out basis.
+
+# Contributing Guide
+
+## Communication
+Before starting work on a major feature, please reach out to us via GitHub, Slack, email, etc. We will make sure no one else is already working on it and ask you to open a GitHub issue.
+A "major feature" is defined as any change that is > 100 LOC altered (not including tests), or changes any user-facing behavior.
+We will use the GitHub issue to discuss the feature and come to agreement.
+This is to prevent your time being wasted, as well as ours.
+The GitHub review process for major features is also important so that organizations with commit access can come to agreement on design.
+If it is appropriate to write a design document, the document must be hosted either in the GitHub tracking issue, or linked to from the issue and hosted in a world-readable location.
+Specifically, if the goal is to add a new extension, please read the extension policy.
+Small patches and bug fixes don't need prior communication.
+
+## Coding Style
+We follow [PEP 8](https://www.python.org/dev/peps/pep-0008/) with one exception: lines can be up to 100 characters in length, not 79.
+We use [scalafmt](https://github.com/databrickslabs/mosaic/blob/main/.scalafmt.conf) to format our Scala code. Please run scalafmt on your code before submitting a pull request.
+
+## Sign your work
+The sign-off is a simple line at the end of the explanation for the patch. Your signature certifies that you wrote the patch 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):
+
+```
+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.
+```
+
+Then you just add a line to every git commit message:
+
+```
+Signed-off-by: Joe Smith <joe.smith@email.com>
+Use your real name (sorry, no pseudonyms or anonymous contributions.)
+```
+
+If you set your `user.name` and `user.email` git configs, you can sign your commit automatically with git commit -s.
 
 ## Repository structure
 The repository is structured as follows: