Merge #1615

1615: Create ISSUE_TEMPLATE.md r=Nebukadneza a=Diman0

Add bug template to be used for reporting issues.

## What type of PR?

Feature?

## What does this PR do?
Add bug template which we will use to get better quality bug reports.

### Related issue(s)
- Auto close an issue like: closes #1331

## Prerequistes
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.

- [N/A] In case of feature or enhancement: documentation updated accordingly
- [N/A] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/guide.html#changelog) entry file.


Co-authored-by: Dimitri Huisman <52963853+Diman0@users.noreply.github.com>
Co-authored-by: Dario Ernst <dario@kanojo.de>

ISSUE_TEMPLATE.md

@@ -0,0 +1,44 @@
+Thank you for opening an issue with Mailu. Please understand that issues are meant for bugs and enhancement-requests.
+For **user-support questions**, reach out to us  on [matrix](https://matrix.to/#/#mailu:tedomum.net).
+
+To be able to help you best, we need some more information.
+
+## Before you open your issue
+- [ ] Check if no issue or pull-request for this already exists.
+- [ ] Check [documentation](https://mailu.io/master/) and [FAQ](https://mailu.io/master/faq.html). (Tip, use the search function on the documentation page)
+- [ ] You understand `Mailu` is made by volunteers in their **free time** — be conscise, civil and accept that delays can occur.
+- [ ] The title of the issue should be short and simple. It should contain specific terms related to the actual issue. Be specific while writing the title.
+
+## Environment & Versions
+### Environment
+ - [ ] docker-compose
+ - [ ] kubernetes
+ - [ ] docker swarm
+
+### Versions
+To find your version, get the image name of a mailu container and read  the version from the tag (example for version 1.7).
+```
+$> docker ps -a | grep mailu
+140b09d4b09c    mailu/roundcube:1.7    "docker-php-entrypoi…"    2 weeks ago    Up 2 days (healthy)    80/tcp
+$> grep MAILU_VERSION docker-compose.yml mailu.env
+```
+
+## Description
+Further explain the bug in a few words. It should be clear what the unexpected behaviour is.  Share it in an easy-to-understand language.
+
+## Replication Steps
+Steps for replicating your issue
+
+## Expected behaviour
+Explain what results you expected - be as specific as possible. Just saying "it doesn’t work as expected" is not useful. It's also helpful to describe what you actually experienced.
+
+## Logs
+Often it is very useful to include log fragments of the involved component. You can get the logs via `docker logs <container name> --tail 1000`. For example for the admin container:
+`docker logs mailu_admin_1 --tail 1000`
+or using docker-compose `docker-compose -f /mailu/docker-compose.yml logs --tail 1000 admin`
+If you can find the relevant section, please share only the parts that seem relevant. If you have any logs, please enclose them in code tags, like so:
+````markdown
+```
+Your logs here!
+```
+````