Add README comment about File Creation Date timezones in file header

We had a bank we work with get persnickety about the File Creation Date being a Saturday for files sent to them on Friday nights
This seemed like it was worth a README warning but not a breaking change to the default value, but let me know if you can think of any code changes to accomodate this for everyone!
We ended up using  in our rails codebase that uses this gem

Author: zcotter

README.md

@@ -1,18 +1,18 @@
-#ACH
+# ACH
 
 [![Build Status](https://travis-ci.org/jm81/ach.svg?branch=master)](https://travis-ci.org/jm81/ach)
 
 ach is a Ruby helper for builder ACH files. In particular, it helps with field
 order and alignment, and adds padding lines to end of file.
 
-**This library has only been used in one production application and for very
+**This library has only been used in two production applications and for very
 limited purposes. Please test thoroughly before using in a production
 environment.**
 
 See [ACH::Builder](http://search.cpan.org/~tkeefer/ACH-Builder-0.03/lib/ACH/Builder.pm)
 for a similar Perl library
 
-##Example
+## Example
 
 You should consult a copy of the [ACH Rules](http://www.nacha.org) for details
 on individual fields. You can probably obtain a copy from your bank.
@@ -30,6 +30,11 @@ fh.immediate_destination = '000000000'
 fh.immediate_destination_name = 'BANK NAME'
 fh.immediate_origin = '000000000'
 fh.immediate_origin_name = 'BANK NAME'
+# Optional - This value is used in the File Creation Date/Time attributes - if excluded will default to Time.now
+# Note that you may wish to modify the time zone here if your environment has a different time zone than the banks
+# For example if your server is in UTC and the bank's is in US/Eastern, any files sent after 8pm Eastern/Midnight UTC
+#   would have a File Creation Date of the next day from the bank's perspective
+fh.transmission_datetime = Time.now
 
 # Batch
 batch = ACH::Batch.new
@@ -73,6 +78,6 @@ ach.batches.first.entries.first.addenda.first.payment_data
 
 **Note:** When adding an amount to your ach file, it needs to be in cents. So you'll want to multiply any dollar amounts by 100
 
-##Copyright
+## Copyright
 
 Copyright (c) 2008-2009 Jared E Morgan, released under the MIT license