readme update

README.md

@@ -1,6 +1,10 @@
 # Saleae Measurements V2
 
-These use Saleae's in-progress V2 measurement API, which has not been released for public use yet. The API used here is expected to change before official release.
+These are a collection of measurement extensions for use with the Saleae Logic software.
+
+Included are basic analog measurements, including vertical measurements like min & max, time measurements like frequency and period, and a few pulse measurements like rise time and overshoot.
+
+This extension package uses Saleae's in-progress V2 measurement API, which has not been released for public use yet. The API used here is expected to change before official release.
 
 ## Voltage Measurements
 
@@ -21,6 +25,8 @@ These use Saleae's in-progress V2 measurement API, which has not been released f
 - Positive Overshoot
 - Negative Overshoot
 
+Rise time and fall time are measured from the 10% crossing point to the 90% crossing point.
+
 ## Time Measurements
 
 - Period