Add back the template

0000-template.md

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+- Feature Name: (fill me in with a unique ident, my_awesome_feature)
+- Start Date: (fill me in with today's date, YYYY-MM-DD)
+- RFC PR: (leave this empty)
+- Rust Issue: (leave this empty)
+
+# Summary
+[summary]: #summary
+
+One para explanation of the feature.
+
+# Motivation
+[motivation]: #motivation
+
+Why are we doing this? What use cases does it support? What is the expected outcome?
+
+# Detailed design
+[design]: #detailed-design
+
+This is the bulk of the RFC. Explain the design in enough detail for somebody familiar
+with the language to understand, and for somebody familiar with the compiler to implement.
+This should get into specifics and corner-cases, and include examples of how the feature is used.
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+Why should we *not* do this?
+
+# Alternatives
+[alternatives]: #alternatives
+
+What other designs have been considered? What is the impact of not doing this?
+
+# Unresolved questions
+[unresolved]: #unresolved-questions
+
+What parts of the design are still TBD?