Add issue template

.gitlab/issue_templates/New Chapter.md

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+Chapter \#
+==========
+
+This is about:
+
+
+## Content
+- [] section x
+  - [] Written
+  - [] Read
+  - [] Review
+  - [] Needs edits
+
+- [] section y
+  - [] Written
+  - [] Read
+  - [] Review
+  - [] Needs edits
+
+- [] section y
+  - [] Written
+  - [] Read
+  - [] Review
+  - [] Needs edits
+
+## Reviewed by:
+ - [] Maureen
+ - [] Daan
+ - [] Tim
+ - [] Jan
+