create RELEASE_SCHEDULE.md (#2255)

* create RELEASE_SCHEDULE.md

* adding slack channel

RELEASE_SCHEDULE.md

@@ -0,0 +1,22 @@
+# Release Schedule
+
+We push a new release of Prebid.js every other week on Tuesday. During the adoption phase for 1.x, we are releasing updates for 1.x and 0.x at the same time.
+
+While the releases will be available immediately for those using direct Git access,
+it will be about a week before the Prebid Org [Download Page](http://prebid.org/download.html) will be updated.  
+
+You can determine what is in a given build using the [releases page](https://github.com/prebid/Prebid.js/releases)
+
+Announcements regarding releases will be made to the #headerbidding-dev channel in subredditadops.slack.com.
+
+# FAQs
+
+**1. Is there flexibility in the 2-week schedule?**
+
+If a major bug is found in the current release, a maintenance patch will be done as soon as possible.
+
+It is unlikely that we will put out a maintenance patch at the request of a given bid adapter or module owner.
+
+**2. What Pull Requests make it into a release?**
+
+Every PR that's merged into master will be part of a release. Here are the [PR review guidelines](https://github.com/prebid/Prebid.js/blob/master/PR_REVIEW.md).