Add contribution guidelines (nrfconnect#10)

Author: deerob4

.github/CONTRIBUTING

@@ -0,0 +1,11 @@
+### Contribution Guidelines
+
+If you or your organization has a project that you'd like to include in the nRF Connect SDK App Index, you can do so by opening a pull request against this repository.
+
+Inside your pull request, create a JSON file named after your GitHub account in the `index` directory (e.g. `index/nrfconnect.json`). Include information about your account or organization, then add an entry for each app you want to be shown in the index to the `apps` array. The `name` field of each app must match a GitHub repository in your account.
+
+If you use Visual Studio Code, the editor will automatically provide validation and autocompletion for the index file. If you are using another editor, you can use the JSON schema located at `resources/schema.json` to validate your file. Make sure that your file correctly follows the schema before creating your pull request, otherwise the CI pipeline will fail.
+
+Make sure that your pull request only adds a new JSON file to the `index` directory, or amends your existing file. Pull requests that make other changes to the repository will be rejected.
+
+Once your pull request is approved and merged, the app index will be rebuilt and republished automatically.

README.md

@@ -2,23 +2,23 @@
 
 An index of applications built for the nRF Connect SDK.
 
-## App Index
+## Contributing
 
-The app index is a JSON file containing organizations and their applications, generated from the contents of the `index` folder. Each JSON file in the folder should be named after the organization's GitHub username (e.g. `nrfconnect.json`), and contain metadata about the organization and its applications according to the schema in `resources/schema.json`.
+If you or your organization has a project that you'd like to include in the nRF Connect SDK App Index, you can open a pull request against this repository. See the details shown in the [`CONTRIBUTING`](.github/CONTRIBUTING) file for more information.
+
+## Development
 
 To build the index file, run `npm run generate-index-json` from the root directory.
 
-## Website
+### Website
 
 This repository includes a static website that displays the contributed applications in a searchable frontend. It's developed using the [Next.js](https://nextjs.org/) React framework, and uses [Tailwind](https://tailwindcss.com/) for styling.
 
-### Development
-
 To launch a live server development server, run `npm run dev` inside the `site` directory. By default, the site runs on port 4000, but this can be overridden by setting the `PORT` environment variable.
 
 Application data is read at build time. For development purposes, sample data can be imported from `sampleData.ts`.
 
-### Building
+#### Building
 
 To build the website, run the following commands:
 
@@ -27,6 +27,6 @@ To build the website, run the following commands:
 
 This will create an optimised static build in the `/site/out` directory.
 
-## Schemas
+### Schemas
 
 JSON schemas are provided to enforce the shape of the data in the index. They are located in the `resources` directory. To edit the schemas, make any changes in `site/src/schema.ts` and run `npm run generate-schemas` from the root directory.