Fixed a typo in the README

README.md

@@ -6,5 +6,5 @@ To use this library, you need a C++ compiler and an installation of
 google or-tools library files.
 
 The environment variable `ORTOOLS_PREFIX` is used to find include
-files and library files. If not setted, `/opt/ortools` will be added
+files and library files. If not set, `/opt/ortools` will be added
 to the search path (classical search path will also be used).