Update issue templates

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a bug report to help us improve Disco.
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behavior, *e.g.* what Disco code produces the error, or what to enter at the Disco REPL prompt to produce the error.
+
+**Expected vs actual behavior**
+What did you expect to happen?  What actually happened instead?
+
+**Screenshots**
+If applicable, you can add screenshots to help explain your problem.
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/confusion-report.md

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+---
+name: Confusion report
+about: Report something that you found confusing!
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+If you found something confusing---for example, the behavior of a Disco function, the wording of a Disco error message *etc.*, please report it here!  It's super helpful to learn what is confusing so that we can make Disco better and easier to understand.  This is also a good place to report something that you think might be a bug, but you're not sure if it's really a bug or just something that you are misunderstanding.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for making Disco better!
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.