perf: Remove unnecessary files from package

This adds all files in the repo that aren't essential to the operation of the package to the
`.npmignore`. This will ensure that things like the `.storybook` directory don't get downloaded
everytime somebody adds NES.css to their project.

.npmignore

@@ -1,3 +1,18 @@
-node_modules
+# User & editor settings
+.editorconfig
+.prettierignore
 .vscode
+
+# Build files
+.circleci
+.github
+.storybook
+commitlint.config.js
+node_modules
+
+# Documentation files
+docs
+favicon.ico
+index.html
 storybook-static
+style.css