Add contributing.md

Signed-off-by: John Collier <[email protected]>

Author: johnmcollier

CONTRIBUTING.md

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+# Contributing to this registry
+
+This document outlines the requirements for contributing a devfile stack or sample to this repository.
+
+The [devfile registry structure](https://github.com/devfile/api/blob/main/docs/proposals/registry/registry-structure.md#repository-structure) design doc provides some useful background information on the structure of resources in a devfile registry (and its Git repository).
+
+## Prerequisites
+
+The following are required to build the devfile index container image containing your stack or sample:
+
+- Docker 17.06 or later
+- Git
+
+## Stacks
+
+### Contributing
+
+1) Verify your Devfile stack functions with odo.
+  
+    - Core odo functions such as `odo create --devfile <devfile.yaml>`, `odo push`, `odo url create` should work with the devfile.
+    - PR tests on this repository will verify this functionality as well.
+
+2) Verify your Devfile stack has the following metadata fields at a minimum:
+
+    - Name: The name of the devfile stack, e.g. `java-springboot`.
+    - Display Name: The longer name of your devfile stack, e.g. `Spring Boot®`.
+    - Description: A brief description of your devfile stack, e.g. `Spring Boot® using Java`.
+    - Version: The version of your stack, in semnatic version format, e.g. `1.0.0`.
+
+2) Add a folder for the stack to `stacks/` in this repository.
+  
+    - Make sure the name matches the devfile stack's name and be in the format `<language>-<framework>`. E.g. `java-quarkus`, `python-django`, etc.
+
+3) Add the devfile.yaml and any other necessary files for the stack under the stack folder.
+
+4) Run the `.ci/build.sh` to build the registry into a container image.
+  
+    - This will also validate the devfiles in this repository, making sure they conform to a minimum standard.
+    - This step will also be run in the PR build for the repository.
+
+5) Open a pull request against this repository with a brief description of the change.
+
+
+### Updating
+
+Updating an existing devfile stack is relatively straightforward:
+
+1) Find the stack under the `stacks/` folder that you wish to update.
+2) Make the necessary changes to the stack, such as: updating image tags, commands, starter projects, etc.
+3) Update the version of stack, following the [semantic versioning format](https://semver.org/).
+4) Test your changes:
+    
+    - Minimally, testing with odo (`odo create`, `odo push`, etc) is recommended, however if your Devfile is used with other tools, it's recommended to test there as well.
+5) Open a pull request against this repository with your changes.
+
+## Samples
+
+### Contributing
+
+The devfile samples used in this devfile registry are stored in the `extraDevfileEntries.yaml` file in the root of the repository. To add a devfile sample:
+
+1) Open `extraDevfileEntries.yaml` in an editor
+2) Add an entry to the file with the following required fields:
+```
+  - name: <sample-name>
+    displayName: <sample-display-name>
+    description: <sample-description>
+    icon: <link-to-sample-icon>
+    tags: ["comma", "separated", "list", "of", "tags"]
+    projectType: <sample-project-type>
+    language: <sample-language>
+    git:
+      remotes:
+        origin: <link-to-sample-git-repository>
+```
+3) Fill in the fields in the angle brackets based on your sample. Note that there must be only one git remote for the devfile sample. 
+4) Open a pull request against this repository with your changes.
+
+### Updating
+
+To update a sample:
+
+1) Open `extraDevfileEntries.yaml` in an editor.
+2) Find the entry for the sample you wish to update.
+3) Make the necessary changes.
+4) Open a pull request against this repository with your changes.