docs: add GitSpo mentions badge

Author: gajus

.README/README.md

@@ -1,5 +1,6 @@
 # eslint-plugin-jsdoc
 
+[![GitSpo Mentions](https://gitspo.com/badges/gajus/eslint-plugin-jsdoc?style=flat-square)](https://gitspo.com/mentions/gajus/eslint-plugin-jsdoc)
 [![NPM version](http://img.shields.io/npm/v/eslint-plugin-jsdoc.svg?style=flat-square)](https://www.npmjs.org/package/eslint-plugin-jsdoc)
 [![Travis build status](http://img.shields.io/travis/gajus/eslint-plugin-jsdoc/master.svg?style=flat-square)](https://travis-ci.org/gajus/eslint-plugin-jsdoc)
 [![js-canonical-style](https://img.shields.io/badge/code%20style-canonical-blue.svg?style=flat-square)](https://github.com/gajus/canonical)