README: Restore RubyGem badge now that twbs owns the "bootstrap" gem

This reverts commit e7b0d726dbe8ad7b442056846b52545e391ace18.
Closes #17022
[ci skip]

1 files changed, 1 insertions, 0 deletions

diff --git a/README.md b/README.md
index e0e7c32bd..201128d4a 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,7 @@
 [![Slack](https://bootstrap-slack.herokuapp.com/badge.svg)](https://bootstrap-slack.herokuapp.com)
 ![Bower version](https://img.shields.io/bower/v/bootstrap.svg)
 [![npm version](https://img.shields.io/npm/v/bootstrap.svg)](https://www.npmjs.com/package/bootstrap)
+[![Gem version](https://img.shields.io/gem/v/bootstrap.svg)](https://rubygems.org/gems/bootstrap)
 [![Build Status](https://img.shields.io/travis/twbs/bootstrap/master.svg)](https://travis-ci.org/twbs/bootstrap)
 [![devDependency Status](https://img.shields.io/david/dev/twbs/bootstrap.svg)](https://david-dm.org/twbs/bootstrap#info=devDependencies)
 [![Meteor Atmosphere](https://img.shields.io/badge/meteor-twbs%3Abootstrap-blue.svg)](https://atmospherejs.com/twbs/bootstrap)