Add the time comparison guideline

Author: pirj

README.adoc

@@ -1808,6 +1808,36 @@ date.all_quarter
 date.all_year
 ----
 
+=== Comparison
+
+Avoid comparing time with `>` and `<` to avoid confusion.
+
+[source,ruby]
+----
+# bad
+created_at < 5.minutes.ago
+shutdown_at > 1.minute.from_now
+
+# good
+created_at.before?(5.minutes.ago)
+shutdown_at.after?(1.minute.from_now)
+----
+
+Use `past?` and `future?` when comparing with the current time.
+
+[source,ruby]
+----
+# bad
+grand_opening_at < Time.current
+public_release_at > Time.current
+
+# good
+grand_opening_at.past?
+public_release_at.future?
+----
+
+NOTE: Rails 6.0 or later is required to use `before?` and `after?`.
+
 == Duration
 
 === Duration Application