Added checklist for new version

Author: grogy

.gitattributes

@@ -10,6 +10,7 @@
 /.travis.yml export-ignore
 /appveyor.yml export-ignore
 /box.json export-ignore
+/doc export-ignore
 /phpcs.xml.dist export-ignore
 /phpcs-ruleset.xml export-ignore
 /tests export-ignore

doc/new-release.md

@@ -0,0 +1,5 @@
+# Checklist for new release
+
+1. change version in `src/Application.php`
+2. add new Git tag
+3. create new version on GitHub with summary of important changes with respect to last version