Create issue_template.md

Reference:
https://github.com/nextcloud/ocsms/blob/master/issue_template.md
https://github.com/stevemao/github-issue-templates/blob/master/checklist2/ISSUE_TEMPLATE.md

issue_template.md

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+<!--
+Thanks for reporting issues back to us!
+To make it possible for us to help you please fill out below information carefully.
+For feature request there is only need for a description.
+-->
+
+### Prerequisites
+* [ ] I searched issues for duplicates
+* [ ] I read the FAQ on README.md
+* [ ] I searched on Internet this issue
+
+### Server configuration
+**OS & version:**
+
+### Client configuration
+**OS & version:**
+
+**Application name & version:**
+
+### Steps to reproduce
+1. [First step]
+2. [Second step]
+3. [and so on ...]
+
+**Actual behavior:**
+
+**Expected behavior:**
+
+**Known solution:**