kdbg: forgot to mention to source prefix.sh before running kdbg

kdbg/README.md

@@ -28,3 +28,13 @@ Install Kdbg. If you want to do a system-wide install, the command below must be
 make install
 ```
 
+To run `kdbg`, simply type `kdbg`.
+
+If you specified an install prefix during the cmake step above (with `-DCMAKE_INSTALL_PREFIX`), then you'll need to source `prefix.sh` before running `kdbg` otherwise it won't work properly:
+
+```
+cp prefix.sh install_dir/kdbg
+source install_dir/kdbg
+install_dir/kdg
+```
+