Improve description of span sink chan capacity
@@ -134,8 +134,9 @@ num_span_workers: 10
# Adjusts the number of spans that can be accomodated before the span
# ingestion buffer blocks. This is good to tweak when you're seeing
-# spiky span ingestion patterns and a lot of spans get dropped. The
-# default for this is no channel capacity.
+# spiky span ingestion patterns and a lot of spans get dropped. This
+# corresponds directly to a Go channel's capacity, for which the
+# default is zero (unbuffered).
span_channel_capacity: 100
# == LIMITS ==
