Add a more useful message when ratelimit is exceeded

Library/Homebrew/utils.rb

@@ -280,10 +280,13 @@ module GitHub extend self
   end
 
   def handle_api_error(e)
-    if e.io.meta['x-ratelimit-remaining'].to_i <= 0
+    if e.io.meta["x-ratelimit-remaining"].to_i <= 0
+      reset = e.io.meta.fetch("x-ratelimit-reset").to_i
+
       raise RateLimitExceededError, <<-EOS.undent, e.backtrace
         GitHub #{Utils::JSON.load(e.io.read)['message']}
-        You may want to create an API token: https://github.com/settings/applications
+        Try again in #{pretty_ratelimit_reset(reset)}, or create an API token:
+          https://github.com/settings/applications
         and then set HOMEBREW_GITHUB_API_TOKEN.
         EOS
     end
@@ -298,6 +301,14 @@ module GitHub extend self
     end
   end
 
+  def pretty_ratelimit_reset(reset)
+    if (seconds = Time.at(reset) - Time.now) > 180
+      "%d minutes %d seconds" % [seconds / 60, seconds % 60]
+    else
+      "#{seconds} seconds"
+    end
+  end
+
   def issues_matching(query, qualifiers={})
     uri = ISSUES_URI.dup
     uri.query = build_query_string(query, qualifiers)