add an example .prettierrc.js config (#3570)
add an example .prettierrc.js config (#3570)

* add an example .prettierrc.js config

* Update configuration.md

existentialism/prettier,prettier/prettier,prettier/prettier,rattrayalex/prettier,rattrayalex/prettier,prettier/prettier,existentialism/prettier,existentialism/prettier,jlongster/prettier,rattrayalex/prettier,existentialism/prettier,prettier/prettier