add Issue template

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,49 @@
+<!--
+
+Provide a general summary of the issue in the Title above
+
+This is a very generic template, remove items that do not apply. For completed items, change [ ] to [x].
+
+-->
+
+### Prerequisites
+
+* [ ] Checked that your issue isn't already filed: https://github.com/strophe/libstrophe/issues?q=
+
+### Additional Information
+
+<!--- Any additional information, configuration or data that might be necessary to reproduce the issue. -->
+
+## Expected Behavior
+
+<!--- If you're describing a bug, tell us what should happen -->
+<!--- If you're suggesting a change/improvement, tell us how it should work -->
+
+## Current Behavior
+
+<!--- If describing a bug, tell us what happens instead of the expected behavior or even better, provide a functional code example reproducing your issue. -->
+<!--- If suggesting a change/improvement, explain the difference from current behavior -->
+
+## Possible Solution
+<!--- Not obligatory, but suggest a fix/reason for the bug, -->
+<!--- or ideas how to implement the addition or change -->
+
+## Steps to Reproduce (for bugs)
+
+<!--- Please either describe your issue in detail or even better, provide a functional code example reproducing your issue. -->
+1.
+2.
+3.
+4.
+
+## Context
+
+<!--- How has this issue affected you? What are you trying to accomplish? -->
+
+## Environment
+
+<!---
+Please provide the version of the library you're using.
+You can find the version either in the first line of the `configure.ac` file or if you're using the Git repository, please run `git describe --always --tags --dirty`.
+Also, please include the compiler, the compiler version, the architecture, the OS and what version of the OS you're experiencing the issue.
+ -->