Add an issue template for new sampler request

.github/ISSUE_TEMPLATE/sampler_proposal.md

@@ -0,0 +1,44 @@
+---
+name: New sampler
+about: Request the implementation of a new sampler.
+title: ''
+labels: ''
+assignees: ''
+---
+
+<!--
+Before suggesting a new sampler, please make sure this hasn't already been suggested by searching through the past issues and the PR tracker.
+-->
+
+### Presentation of the new sampler
+
+<!--
+Assume that we know nothing about this sampler. Please give us as much information as possible so we can judge it fairly. That includes (but is not limited to):
+- Academic article
+- Blog posts
+- Implementations
+- Personnal experience with the algorithm
+-->
+
+### How does it compare to other algorithms in blackjax?
+
+<!--
+How does it compare in terms of
+- Performance
+- Generality
+- Complexity
+-->
+
+### Where does it fit in blackjax
+
+<!--
+Please explain to us why you are suggesting this algorithm for integration with blackjax.
+-->
+
+### Are you willing to open a PR?
+
+<!--
+Tell us whether you are willing to implement the algorithm yourself, and if so if you can share a design plan.
+-->
+
+<!-- Thanks for contributing! -->