meta: add pull request template (#940)

Author: dingsdax

.github/pull_request_template.md

@@ -0,0 +1,13 @@
+### Description
+<!-- What changed and why? -->
+
+#### Issues
+<!--
+* resolves: #1234
+* resolves: LIN-1234
+-->
+
+#### Reminders
+- Add GH Issue ID _&_ Linear ID
+- PR title should use [conventional commit](https://develop.sentry.dev/engineering-practices/commit-messages/#type) style (`feat:`, `fix:`, `ref:`, `meta:`)
+- For external contributors: [CONTRIBUTING.md](../CONTRIBUTING.md), [Sentry SDK development docs](https://develop.sentry.dev/sdk/), [Discord community](https://discord.gg/Ww9hbqr)