Add CONTRIBUTING information and templates

Guidelines for developers and users describing how they can
participle in the project.

Reviewed-by: Manuel Mendez <mmendez534@gmail.com>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: George Melikov <mail@gmelikov.ru>
Closes #672 
Closes #4776  
Closes #5361

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,37 @@
+<!--
+Thank you for reporting an issue.
+
+This issue tracker is for bugs and issues only.
+If you need general support please use 
+our mailing list. https://github.com/zfsonlinux/zfs/wiki/Mailing-Lists
+
+Please fill in as much of the template as possible.
+-->
+
+### System information
+<!--  add version after "|" character -->
+Type                                | Version/Name
+  ---                                  |     --- 
+Distribution Name       | 
+Distribution Version    | 
+Linux Kernel                 | 
+Architecture                 | 
+ZFS Version                  | 
+SPL Version                  | 
+<!-- 
+Commands to find ZFS/SPL versions:
+modinfo zfs | grep -iw version
+modinfo spl | grep -iw version 
+-->
+
+### Describe the problem you're observing
+
+### Describe how to reproduce the problem
+
+### Include any warning/errors/backtraces from the system logs
+<!-- 
+Example:
+```
+this is an example how log text should be marked (wrap it with ```)
+```
+-->