Update README.md

Add license icon to readme.

README.md

@@ -21,3 +21,5 @@ This TeX source is released under a [Creative Commons Attribution–ShareAlike 4
 
 To ensure compliance with the CC BY-SA 4.0 licence, if you want to modify or adapt the TeX source for your own use, please update the `\adaptername` and `\adapteremail` commands in the `infdesc.tex` file with your name and email address, respectively. This will automatically take care of all necessary attributions, and will cite you as the adapter on the title page and copyright page.
 
+### License 
+<a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by-sa/4.0/88x31.png" /></a><br />This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International License</a>.