Added issue template

ISSUE_TEMPLATE.md

@@ -0,0 +1,30 @@
+### Expected behavior
+
+Tell us what should happen
+
+### Actual behavior
+
+Tell us what happens instead.
+
+### System configuration
+
+- net-ssh version
+- Ruby version
+
+### Example App
+
+Please provide an example script that reproduces the problem. This will save maintainers time so they can spend it fixing your issues instead of trying to build a reproduction case from sparse instructions.
+
+You can use this as stating point:
+
+```ruby
+gem 'net-ssh', '= 4.0.0.beta3'
+require 'net/ssh'
+puts Net::SSH::Version::CURRENT
+
+@host = 'localhost'
+@user = ENV['USER']
+Net::SSH.start(@host, @user) do |ssh|
+  puts ssh.exec!('echo "hello"')
+end
+```