Add sample rate to SDK docs. (#104)

Author: bretthoerner

docs/clientdev/overview.rst

@@ -32,6 +32,7 @@ Additionally, the following features are highly encouraged:
 * Non-blocking event submission
 * Basic data sanitization (e.g. filtering out values that look like passwords)
 * Context data helpers
+* Event sampling
 
 Usage for End-users
 -------------------
@@ -132,6 +133,20 @@ The resulting POST request would then transmit to::
 .. note:: If any of configuration values are not present, the SDK should notify the user
           immediately that they've misconfigured the SDK.
 
+Event Sampling
+--------------
+
+SDKs should allow the user to configure what percentage of events are actually
+sent to the server (the rest should be silently ignored). For example:
+
+.. sourcecode:: python
+
+    sample_rate = options.get('sample_rate', 1.0)
+
+    # assuming random() returns a value between 0.0 (inclusive) and 1.0 (exclusive)
+    if random() < sample_rate:
+        raven.send(data)
+
 Building the JSON Packet
 ------------------------