Update issue templates (#683)

Author: axunonb

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,40 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: bug
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+
+1. iCalendar Data
+If possible, provide the iCalendar data that reproduces the issue:
+```
+BEGIN:VCALENDAR
+...
+END:VCALENDAR
+```
+
+2. Include a unit test that shows actual and expected behavior:
+```cs
+var calendar = Calendar.Load("...");```
+---
+Assert.That(...)
+```
+
+**Expected behavior**
+Add a clear and concise description for the reason of the expected behavior.
+
+**Environment (please complete the following information):**
+- OS: [e.g. Windows 10, macOS 11.2]
+- .NET version: [e.g. .NET 6, .NET Framework 4.8]
+- ical.net version: [e.g. 4.1.0]
+
+**Additional context**
+Add any other context about the problem here, such as relevant code snippets, logs, or error messages.