added URL to readme

Author: aerler

README.md

@@ -2,4 +2,4 @@
 Tools and scripts to set up and run climate simulations with WRF.
 
 A high-level description of different modules and their functionality is available in PDF format:
-Docs/Thesis Excerpt/wrftools.pdf
+[Docs/Thesis Excerpt/wrftools.pdf](https://github.com/aerler/WRF-Tools/blob/master/Docs/Thesis%20Excerpt/wrftools.pdf)