update PR template to include link to dev docs page (prebid#1075)

.github/PULL_REQUEST_TEMPLATE.md

@@ -6,7 +6,7 @@ Thank you for your pull request. Please make sure this PR is scoped to one chang
 <!-- Remove items that don't apply and/or select an item by changing [ ] to [x] -->
 - [ ] Bugfix
 - [ ] Feature
-- [ ] New bidder adapter
+- [ ] New bidder adapter  <!--  IMPORTANT: if checking here, also submit your bidder params documentation here https://github.com/prebid/prebid.github.io/tree/master/dev-docs/bidders --> 
 - [ ] Code style update (formatting, local variables)
 - [ ] Refactoring (no functional changes, no api changes)
 - [ ] Build related changes