Update README.md

Author: martin-henz

README.md

@@ -12,7 +12,7 @@ https://github.com/source-academy/sicp/wiki
 ## Licenses
 
 [![CC BY-SA 4.0][cc-by-sa-image]][cc-by-sa] 
-This work is licensed under a [Creative Commons Attribution-ShareAlike 4.0
+This work is licensed under the [Creative Commons Attribution-ShareAlike 4.0
 International License][cc-by-sa].
 
 [![GPL 3][gpl3-image]][gpl3]