add template for installer issues

since the installer prompts users to file issues, labelling them
automatically should reduce triaging effort significantly.

.github/ISSUE_TEMPLATE/installer.md

@@ -0,0 +1,36 @@
+---
+name: Installer issue
+about: Report problems with installation
+title: ''
+labels: installer
+assignees: ''
+
+---
+
+## Platform
+
+<!-- select the platform on which you tried to install Nix -->
+
+- [ ] Linux: <!-- state your distribution, e.g. Arch Linux, Ubuntu, ... -->
+- [ ] macOS
+- [ ] WSL
+
+## Additional information
+
+<!-- state special circumstances on your system or additional steps you have taken prior to installation -->
+
+## Output
+
+<details><summary>Output</summary>
+
+```log
+
+<!-- paste console output here and remove this comment -->
+
+```
+
+</details>
+
+## Priorities
+
+Add :+1: to [issues you find important](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc).

scripts/install-multi-user.sh

@@ -97,7 +97,8 @@ is_os_darwin() {
 }
 
 contact_us() {
-    echo "You can open an issue at https://github.com/nixos/nix/issues"
+    echo "You can open an issue at"
+    echo "https://github.com/NixOS/nix/issues/new?labels=installer&template=installer.md"
     echo ""
     echo "Or feel free to contact the team:"
     echo " - Matrix: #nix:nixos.org"