meta: add legal boilerplate to PR template (#3089)

Added legal boilerplate to clarify contribution rights b/c CLI is FSL

Co-authored-by: Daniel Szoke <daniel.szoke@sentry.io>

Author: dingsdax

.github/pull_request_template.md

@@ -14,5 +14,5 @@
 - For external contributors: [CONTRIBUTING.md](https://github.com/getsentry/sentry-cli/blob/master/CONTRIBUTING.md), [Sentry SDK development docs](https://develop.sentry.dev/sdk/), [Discord community](https://discord.gg/Ww9hbqr)
 -->
 
-
-
+### Legal Boilerplate
+Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.