Improve documentation (#349)

* Improve documentation content
* Improve documentation style

docs/docs/index.mdx

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+---
+sidebar_position: 0
+hide_title: true
+sidebar_class_name: display-none
+title: Welcome
+custom_edit_url: null
+---
+import ThemedImage from '@theme/ThemedImage';
+
+# Introduction
+
+Twenty is an Open Source CRM.
+<ThemedImage sources={{light: "./img/preview-docs-light.png", dark:"./img/preview-docs-dark.png"}} style={{width:'100%', maxWidth:'800px'}}/>
+
+
+## Why did we create Twenty?
+At first, CRM platforms were just for sales teams.
+But now, they've grown to cover more than just sales - they handle many aspects of running a business.
+This has often left in-house engineering teams out of the loop, making companies rely more on outside help to manage their CRM needs.
+
+Our team has a shared passion for crafting beautiful product with great attention to details.
+And we are starting this project with one key goal: to put the power back in the hands of the people who use CRM systems every day.
+We wish to create a tool that users will enjoy, and that engineers will want to make their own and customize for their company's specific needs.
+
+## Getting started
+
+There are three ways for you to get started which are documented in the left sidebar:
+- **Cloud:** the fastest and easiest way to try the app (it's free)
+- **Local:** if you're a developer and would like to experiment or contribute to the app
+- **Self-hosting:** if you want greater control over your data and to run the app on your own server
+
+## Contributing
+Contributions are what makes the open source community such an amazing place.  
+Code contributions through pull request are most welcome.
+But it doesn't have to be code. You can also create an issue to report a bug you've spotted, join discussions or write documentation.
+
+