Add GitHub support file (#151)

* Add GitHub support file

Shown to users when before they submit a new issue

* Add elixir_sense issues

Author: axelson

.github/SUPPORT.md

@@ -0,0 +1,36 @@
+# Support
+
+Thank you for using ElixirLS! :tada:
+
+This document offers some guidelines when asking for support related to an
+issues that you might encounter when using ElixirLS.
+
+# Guidelines
+
+These are some general guidelines to follow when reaching out through any of the
+available support channels.
+
+1. **Search through the existing
+   [issues](https://github.com/elixir-lsp/elixir-ls/issues/) before opening a new
+   one**
+
+   Also check [elixir\_sense issues](https://github.com/elixir-lsp/elixir_sense/issues)
+
+   Check if one already exists related to the issue you are having. Remember
+   to include `closed` issues as well.
+
+2. **Provide as much context and information as possible**
+
+   It is much more likely that others will be able to help you if they can
+   reproduce the issue your are experiencing.
+
+3. **Be nice**
+
+   This can be applied to life in general, but it's especially important when
+   communicating only through written text.
+
+# Support Channels
+
+- Github [Issues](https://github.com/elixir-lsp/elixir-ls/issues/).
+- #elixir-ls tag on the [elixir forum](https://elixirforum.com/).
+