add readings-per-sec.csv file to gitignore.

It was getting in the way and doesn't need to be part of the commit
history. It's only purpose is to output the results -- to be used else
where.

.gitignore

@@ -138,3 +138,4 @@ dmypy.json
 # Cython debug symbols
 cython_debug/
 
+/src/data/results/

src/data/results/readings-per-sec.csv

@@ -1,4 +0,0 @@
-1,5344
-2,2955
-3,13284
-4,8297