README: add badge indicating development status

Using the Trove classifiers scheme
(same as PyPI; see https://pypi.python.org/pypi?%3Aaction=list_classifiers)

[ci skip]

1 files changed, 1 insertions, 0 deletions

diff --git a/README.md b/README.md
index b721475..873185b 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,7 @@
 Rorschach
 =========
 [![Build Status](https://travis-ci.org/twbs/rorschach.svg?branch=master)](https://travis-ci.org/twbs/rorschach)
+![Development Status :: 5 - Production/Stable](https://img.shields.io/badge/maturity-stable-green.svg "Development Status :: 5 - Production/Stable")
 [![MIT License](https://img.shields.io/github/license/twbs/rorschach.svg)](https://github.com/twbs/rorschach/blob/master/LICENSE.txt)
 
 Rorschach ([@twbs-rorschach](https://github.com/twbs-rorschach)) is a [Bootstrap](https://github.com/twbs/bootstrap/) pull request sanity checker bot.