Fix issue #85: prettier configuration to format .astro files

.prettierrc.js

@@ -0,0 +1,13 @@
+/** @type {import('prettier').Config} */
+module.exports = {
+  printWidth: 120,
+  semi: true,
+  singleQuote: true,
+  tabWidth: 2,
+  trailingComma: 'es5',
+  useTabs: false,
+
+  plugins: [require.resolve('prettier-plugin-astro')],
+
+  overrides: [{ files: '*.astro', options: { parser: 'astro' } }],
+};