update vignette to emphasise that count_foci and measure_distances_general...

update vignette to emphasise that count_foci and measure_distances_general find the coincident foci mask with the exact same input parameters, and it is much faster to play around with/ calibrate your input parameters with count_foci, since at the moment measure_distances_general is relatively very slow

vignettes/synapsis_tutorial_v1.Rmd

@@ -281,5 +281,5 @@ t.test(as.numeric(distance_KO),as.numeric(distance_WT))
 
 ## .nd2 files
 
-## 3 channel / false colour jpeg, tiff or pngs
+## 3 channel / false colour jpeg, tif or pngs