docs: Add prettier support

Official guidelines:
https://prettier.io/docs/en/install.html
https://prettier.io/docs/en/integrating-with-linters.html
https://github.com/prettier/eslint-config-prettier

Steps taken:
npm install --save-dev --save-exact prettier
Create .prettierignore
Create .prettierrc.js
npm install --save-dev eslint-config-prettier
Edit .eslintrc.js

docs/.prettierrc.js

@@ -0,0 +1 @@
+module.exports = {};