Add missing closing brackets for code block

Author: francescolofranco

README.md

@@ -45,4 +45,5 @@ Additional options can be passed to the `install-packages` target:
 make install-packages opts="--with dev"
 
 # Install with specific extras
-make install-packages opts="--extras 'feature1 feature2'"
+make install-packages opts="--extras 'feature1 feature2'"
+```