Added eleventy config

Added input and output directories and set the templating engine to nunjucks

.eleventy.js

@@ -0,0 +1,10 @@
+module.exports = function(eleventyConfig) {
+
+  return {
+    dir: {
+      input: 'src',
+      output: '_site',
+    },
+    markdownTemplateEngine: 'njk'
+  }
+}