Update issue templates

.github/ISSUE_TEMPLATE/add-a-reader-s-cluster.md

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+---
+name: Add a Reader's Cluster
+about: Describe this issue template's purpose here.
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+## Reader's cluster request
+
+My cluster is:
+
+- [ ] A blog post
+- [ ] A photo Tweet
+
+I have given attribution and linked / referenced any blog posts or images that I've used as part of the submission
+
+- [ ] Yes
+- [ ] No
+
+Please give the URL below:
+
+Title for blog post or Tweet:
+
+Your name: