Fix Readme spelling mistakes

README.md → Readme.md

@@ -5,14 +5,14 @@ The HCI Theme packaged as a gem.
 
 ## Installation
 
-Add this line to your Jekyll site's `Gemfile`:
+Add these lines to your Jekyll site's `Gemfile`:
 
 ```ruby
 gem "hci-theme", :git => "git@gitlab2.informatik.uni-wuerzburg.de:hci-development/hci-theme.git"
 gem "jekyll-img-srcset", :git => "git@gitlab2.informatik.uni-wuerzburg.de:hci-development/jekyll-img-srcset.git"
 ```
 
-And add this line to your Jekyll site's `_config.yml`:
+And add these lines to your Jekyll site's `_config.yml`:
 
 ```yaml
 theme: hci-theme