Add bug report issue template (#448)

As we repeatedly ask for information about users' environments, I added this template

Co-authored-by: Norwin <git@nroo.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/448
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Norwin <noerw@noreply.gitea.io>
Co-committed-by: Norwin <noerw@noreply.gitea.io>

.gitea/issue_template/bug.md

@@ -0,0 +1,30 @@
+---
+name: "Bug Report"
+about: "Use this template when reporting a bug, so you don't forget important information we'd ask for later."
+title: "Bug: "
+labels: 
+- kind/bug
+---
+
+### describe your environment
+- tea version used (`tea -v`):
+    - [ ] I also reproduced the issue [with the latest master build](https://dl.gitea.io/tea/master)
+- Gitea version used:
+    - [ ] the issue only occured after updating gitea recently
+- operating system:
+- I make use of...
+    - [ ] non-standard default branch names (no `main`,`master`, or `trunk`)
+    - [ ] .ssh/config or .gitconfig host aliases in my git remotes
+    - [ ] ssh_agent or similar
+    - [ ] non-standard ports for gitea and/or ssh
+    - [ ] something else that's likely to interact badly with tea: ...
+
+
+Please provide the output of `git remote -v` (if the issue is related to tea not finding resources on Gitea):
+```
+
+```
+
+### describe the issue (observed vs expected behaviour)
+
+