Setting up prettier

In order not to wreak havoc on all the open PRs, Prettier will be added slowly,
on every changed file, thanks to Husky (for a precommit hook) and lint-staged, for linting only staged files.

package.json

@@ -0,0 +1,8 @@
+{
+  "devDependencies": {
+    "husky": "^6.0.0"
+  },
+  "scripts": {
+    "prepare": "husky install"
+  }
+}