[docs] Correction for Zedmon sample rate

The current README claims Zedmon supports up to 3.5 KHz sample rate. In
reality, the max sample rate is 1.5 KHz.

Change-Id: I7538360407a8f9c01d0e960725c0da964fd7a324
Reviewed-on: https://fuchsia-review.googlesource.com/c/zedmon/+/633222
Reviewed-by: Onath Dillinger <claridge@google.com>

README.md

diff --git a/README.md b/README.md
index 4ee025b..1adf1cb 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@
 
  * Can monitor up to 5A@28V (36V in upcoming rev 2).
  * 0.25 mA resolution.
- * Up to 3.5 KHz sample rate.
+ * Up to 1.5 KHz sample rate.
  * Current sense circuitry isolated from USB interface.
  * High and Low side sensing for detecting ground loops.
  * Relay on power line for enabling/disabling power to the device under test.