style of icon

README.md

@@ -25,7 +25,7 @@ In order to use the slide deck, you must have:
     $ contribute --date="YYYY-MM-DD" --name="yourAwesomeTitle"
     ```
 
-<img src="https://webdav-r3lab.uni.lu/public/R3lab/logos/warning.png"> Please create a branch from `develop` before starting to work on your presentation. You could name it `YYYY-MM-DD_yourAwesomeTitle`.
+<img src="https://webdav-r3lab.uni.lu/public/R3lab/logos/warning.png" height="20px" width="20px"> Please create a branch from `develop` before starting to work on your presentation. You could name it `YYYY-MM-DD_yourAwesomeTitle`.
 
 If you are done with making changes to your presentation, push them to your fork and open a merge request against the `develop` branch.