fix: readme implies wrong composer require command (#403)

require accept multiple packages as arguments, using a space will tell composer to install both fof/upload and "*". Using the : delimiter will help it understand the wildcard as version constraint.

README.md

@@ -22,13 +22,13 @@ An extension that handles file uploads intelligently for your forum.
 Install manually:
 
 ```sh
-composer require fof/upload "*"
+composer require fof/upload:"*"
 ```
 
 ## Updating
 
 ```sh
-composer require fof/upload "*"
+composer require fof/upload:"*"
 php flarum migrate
 php flarum cache:clear
 ```