Update README.md

Fix directory name.

README.md

@@ -60,7 +60,7 @@ The switch makes use of the NetBee library to parse packets, so we need to insta
     ```
 
 ## Building
-Run the following commands in the `of13softswitch` directory to build and install everything:
+Run the following commands in the `ofsoftswitch13` directory to build and install everything:
 
     $ ./boot.sh
     $ ./configure