Add an example to the readme

Author: fhunleth

README.md

@@ -7,6 +7,30 @@
 
 CircularBuffer provides a general-purpose circular buffer data structure.
 
+```elixir
+# Create a new circular buffer that holds 5 elements
+iex> cb = CircularBuffer.new(5)
+#CircularBuffer<[]>
+
+# Fill it up
+iex> cb = Enum.into(1..5, cb)
+#CircularBuffer<[1, 2, 3, 4, 5]>
+
+# Verify that 1 is the oldest and 5 is the newest element in the buffer
+iex> CircularBuffer.oldest(cb)
+1
+iex> CircularBuffer.newest(cb)
+5
+
+# Add another element. 1 gets pushed out.
+iex> cb = CircularBuffer.insert(cb, 6)
+#CircularBuffer<[2, 3, 4, 5, 6]>
+
+# CircularBuffer implements Enumerable so all Enum.* functions work
+iex> Enum.sum(cb)
+20
+```
+
 ## Installation
 
 ```elixir
@@ -19,7 +43,7 @@ end
 
 ## Should I use this?
 
-The entire codebase is less than 50 lines of code and has been tested using
-property based testing. I believe the implementation is sound but it may not
-be the highest performance library out there.
-
+The entire codebase is about 70 lines of code, has been tested using property
+based testing, and has been used in production for several years. I believe the
+implementation is sound but it may not be the highest performance library out
+there.