docs: add a pull request template

This repo had none, so PR bodies arrive with no structure. Uses the same
foundry-derived template as seaport and seadrop, with all guidance inside HTML
comments so nothing renders except the two headings the author fills in.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: ryanio

.github/pull_request_template.md

@@ -0,0 +1,28 @@
+<!--
+Borrowed from foundry.
+
+Thank you for your Pull Request. Please provide a description above and review
+the requirements below.
+
+Bug fixes and new features should include tests.
+
+Do not report security vulnerabilities in a public pull request or issue. Use
+https://bugcrowd.com/engagements/opensea instead.
+-->
+
+## Motivation
+
+<!--
+Explain the context and why you're making that change. What is the problem
+you're trying to solve? In some cases there is not a problem and this can be
+thought of as being the motivation for your change.
+
+If your PR solves a particular issue, tag that issue.
+-->
+
+## Solution
+
+<!--
+Summarize the solution and provide any necessary context needed to understand
+the code change.
+-->