adjusted install guide

Author: jonasjabari

docs/guides/1-installation/README.md

@@ -7,7 +7,7 @@ This guide shows you how to add matestack-ui-core to an existing rails applicati
 Add 'matestack-ui-core' to your Gemfile
 
 ```ruby
-gem 'matestack-ui-core'
+gem 'matestack-ui-core', '>= 1.0.0.rc.1'
 ```
 
 and run
@@ -27,7 +27,7 @@ Rails 6+ apps, by default, use webpacker, rails 5 apps, by default, use the asse
 Add 'matestack-ui-core' to your `package.json` by running:
 
 ```
-$ yarn add https://github.com/matestack/matestack-ui-core#v1.0.0
+$ yarn add https://github.com/matestack/matestack-ui-core#v1.0.0.rc.1
 $ yarn install
 ```