docs: add Project Setup section to Developer Guide (#2780)

Co-authored-by: Flo Edelmann <git@flo-edelmann.de>

Author: 2nofa11

docs/developer-guide/index.md

@@ -8,6 +8,15 @@ If you think you’ve found a bug in ESLint, please [create a new issue](https:/
 
 Please include as much detail as possible to help us properly address your issue. If we need to triage issues and constantly ask people for more detail, that’s time taken away from actually fixing issues. Help us be as efficient as possible by including a lot of detail in your issues.
 
+## :seedling: Project Setup
+
+To develop locally, fork the eslint-plugin-vue repository and clone it in your local machine. Use the [npm](https://www.npmjs.com/) package manager to install and link dependencies and the LTS version of [Node.js](https://nodejs.org/).
+
+To develop and test the `eslint-plugin-vue` package:
+
+1. Run `npm install` in the project's root folder.
+2. Run `npm test` to make sure everything is set up correctly.
+
 ## :sparkles: Proposing a new rule or a rule change
 
 In order to add a new rule or a rule change, you should: