Correct endless range example and provide some clarity

Resolves #321

Author: Justin Dell

README.adoc

@@ -1069,11 +1069,17 @@ User.where("created_at > :start AND created_at < end", start: 30.days.ago, end:
 User.where(created_at: 30.days.ago..7.days.ago)
 
 # bad
-User.where("created_at > ?", 7.days.ago)
+User.where("created_at >= ?", 7.days.ago)
 
 # good
 User.where(created_at: 7.days.ago..)
 
+# note - ranges are inclusive or exclusive of their ending, not beginning
+User.where(created_at: 7.days.ago..)  # produces >=
+User.where(created_at: 7.days.ago...) # also produces >=
+User.where(created_at: ..7.days.ago)  # inclusive: produces <=
+User.where(created_at: ...7.days.ago) # exclusive: produces <
+
 # okish - there is no range syntax that would denote inclusion on one end and
 # exclusion on another.
 Customer.where("purchases_count > :min AND purchases_count <= :max", min: 0, max: 5)