Remove redundant installation info lines

Why do we even have this ~~lever~~ line? 

Looks like a bit of oversight when we consolidated docs and updated for stable. Probably made sense at the time, now we have installation docs that we keep up to date. Remove this line to prevent confusion because it's out of date.

README.md

@@ -21,13 +21,7 @@
 
 ## Installation
 
-You must have SSH access to a server with **PHP 7.3+** and **MySQL 5.6+** or **MariaDB 10.0.5+**, and install [Composer](https://getcomposer.org/).
-
-```
-composer create-project flarum/flarum . --stability=beta
-```
-
-Read the **[Installation guide](https://flarum.org/docs/install.html)** for more information. For support, refer to the [documentation](https://flarum.org/docs/), and ask questions on the [community forum](https://discuss.flarum.org/) or [Discord chat](https://flarum.org/discord/).
+Read the **[Installation guide](https://flarum.org/docs/install.html)** to get started. For support, refer to the [documentation](https://flarum.org/docs/), and ask questions on the [community forum](https://discuss.flarum.org/) or [Discord chat](https://flarum.org/discord/).
 
 ## Contributing