Use a markdown issue template instead of YAML.

The YAML template isn't showing up and there's no indication from
GitHub about why. It's apparently a new preview feature, so I'm
hoping the markdown file works better.

.github/ISSUE_TEMPLATE/website-or-docs-suggestion.md

@@ -0,0 +1,18 @@
+---
+name: Website or Documentation Suggestion
+about: For issues and suggestions for https://block.github.io/elasticgraph/
+title: "[Website] <Title Here>"
+labels: ["good first issue", "help wanted", "website"]
+---
+
+**Suggest an improvement**
+*A clear and concise description of what you'd like to see improved.*
+
+**URLs of impacted pages**
+*Provide the URLs of the pages you'd like to see improved, if your suggestion applies to existing pages.*
+
+**Screenshots**
+*Please provide screenshots if your suggestion relates to how the site looks.*
+
+**Additional context**
+*Add any other context that you feel is relevant about the problem here.*