Consistent executable path in README.md

These commands run (from the source directory; would commands as run
from the build directory be clearer?) for me as-is (after the testbed
executable has been built) now.

README.md

@@ -72,19 +72,19 @@ Running the Examples
 
 Load data points from a file:
 ```
-p2t <filename> <center_x> <center_y> <zoom>
+build/testbed/p2t <filename> <center_x> <center_y> <zoom>
 ```
 Random distribution of points inside a constrained box:
 ```
-p2t random <num_points> <box_radius> <zoom>
+build/testbed/p2t random <num_points> <box_radius> <zoom>
 ```
 Examples:
 ```
-./build/p2t testbed/data/dude.dat 300 500 2
-./build/p2t testbed/data/nazca_monkey.dat 0 0 9
+build/testbed/p2t testbed/data/dude.dat 300 500 2
+build/testbed/p2t testbed/data/nazca_monkey.dat 0 0 9
 
-./build/p2t random 10 100 5.0
-./build/p2t random 1000 20000 0.025
+build/testbed/p2t random 10 100 5.0
+build/testbed/p2t random 1000 20000 0.025
 ```
 
 References