Update README with large file guidelines

Fixes devopsdays#158

README.md

@@ -51,3 +51,11 @@ All logos will be constrained, via markup, to 100px square; combined with the im
 ## Speakers & Program
 
 The program is driven by the program.md file in your event (copied from the [sample program.md](https://raw.githubusercontent.com/devopsdays/devopsdays-web/master/content/events/sample-event/program.md). To generate a data-driven program, look at the Minneapolis 2016 [speakers data files](https://github.com/devopsdays/devopsdays-web/tree/master/data/speakers/2016/minneapolis) and [program directory](https://github.com/devopsdays/devopsdays-web/tree/master/content/events/2016-minneapolis/program).
+
+## Binary files
+
+Generally speaking, you should avoid storing any files other than logos or small images inside the repo itself (out of consideration for your fellow devopsdays organizers who have to pull down this repo). Please follow these guidelines:
+
+- Do not upload presentations, artifacts from your event, etc. Either link to the preso on Speakerdeck/Slideshare from the presenter, or even better, create a Speakerdeck account for your event and put the presos there.
+- Small, web images are fine (logos, etc). If you have high-resolution versions of your logo to share with others, please do not host them on the devopsdays-web repo.
+- It is acceptable to add in a single PDF for your sponsor prospectus if you desire (in `/static/events/YYYY-city`), but please keep this file under 3 MB. It is better to host it on Google Drive or something similar, and then link to it from your site.