Add SECURITY.md and new issue templates

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -0,0 +1,53 @@
+name: Bug report
+about: Please only create issues for bug reports. Feature requests or general questions should start as a "Discussion" on GitHub.
+body:
+  - type: markdown
+    attributes:
+      value: Please make sure to search our issues for similar bugs first! If bug has been reported already, react with a thumbs-up, and/or leave a comment providing further details.
+  - type: textarea
+    id: current
+    attributes:
+      label: Problem and impact
+      description: What problem you're running into? What impact does it have on you / your event?
+      placeholder: When trying to do ____, pretix suddenly shows me an error saying "...".
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected behaviour
+      description: Sometimes bugs are subtle and the expected behaviour may need some explanation. Leave empty if it's just "Don't be broken."
+  - type: textarea
+    id: reproduction
+    attributes:
+      label: Steps to reproduce
+      description: "Please give as much context as possible: Are there any settings that impact this behaviour?"
+      placeholder: |
+        1.
+        2.
+        3.
+        4.
+  - type: textarea
+    id: screenshots
+    attributes:
+      label: Screenshots
+      description: If possible, show screenshots of the problem.
+  - type: input
+    id: link
+    attributes:
+      label: Link
+      description: Link to the page where the bug occurs
+  - type: input
+    id: browser
+    attributes:
+      label: Browser (software, desktop or mobile?) and version
+      description: Leave empty for backend problems
+  - type: input
+    id: os
+    attributes:
+      label: Operating system, dependency versions
+      description: Leave empty for frontend problems
+  - type: input
+    id: version
+    attributes:
+      label: Version
+      description: The pretix version in use. (Leave empty if unknown.)
+