Add an issue template to the project (#185)

This patch adds a template for Issues opened against the
gas project. That way, minimum information is present to debug
the problem.

Signed-off-by: Eric Brown <[email protected]>

Author: ericwb

.github/issue_template.md

@@ -0,0 +1,13 @@
+### Summary 
+
+### Steps to reproduce the behavior
+
+### Gas version
+
+### Go version (output of 'go version')
+
+### Operating system / Environment
+
+### Expected behavior
+
+### Actual behavior