Supplying your SteamID in an email to firstname.lastname@example.org will help the devs troubleshoot any missing items or contents you may be entitled to, specifically if you were a previous Founder.
Finding Your Steam ID
To find your SteamID, simply view your Steam profile (drop down menu in the top right corner of Steam interface.) Right click and Copy Page URL. Now open up a browser window and paste the address into the URL.
Your Steam profile should consist of a long 17 or so digit number that begins with a 7. This number is your SteamID.
If You Have a Custom SteamID
If you have a custom SteamID, refer to this website: http://steamidfinder.com/
Insert your custom Steam Profile URL and press enter, and you will receive a code that resembles STEAM_0:0:XXXXXXXX.
Simply run the STEAM_0:0:XXXXXXXX number again through the initial SteamID search box and it should yield the traditional 17 digit number that begins with a 7.
If you have any issues, make a post here http://steamcommunity.com/app/251970/discussions/5/
Alternatively, Manny can probably find your SteamID for you and give it directly to the devs if need be.