Add note on CI failures in PR template

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,5 +1,5 @@
 Checklist:
-- [ ] Meaningful commit message, eg `add my-cool-package` (please not mention `build-constraints.yml`)
+- [ ] Meaningful commit message, eg `add my-cool-package` (please don't mention `build-constraints.yml`)
 - [ ] At least 30 minutes have passed since uploading to Hackage
 - [ ] On your own machine, you have successfully run the following command (find verify-package in the root of this repo):
 
@@ -11,3 +11,12 @@ The script runs virtually the following commands in a clean directory:
       cd $package-$version
       rm -f stack.yaml && stack init --resolver nightly --ignore-subdirs
       stack build --resolver nightly --haddock --test --bench --no-run-benchmarks
+
+
+### CI
+
+Our CI tries to line up build-constraints.yaml with the current state
+of Hackage. This means that failures that are unrelated to your PR may
+cause the check to fail. If you think a failure is unrelated you can
+simply ignore it and the Curators will let you know if there is
+anything you need to do.