README.md: Add CI badge

Signed-off-by: Ce Gao <ce.gao@outlook.com>

Author: gaocegege

readme.md

@@ -5,7 +5,9 @@
 
 <h4 align="center">Processing.R allows the users to write Processing sketches in R.</h4>
 
-***Notice: Now Processing.R is still in early development stage, not production ready!***
+[![Build Status](https://travis-ci.org/gaocegege/Processing.R.svg?branch=master)](https://travis-ci.org/gaocegege/Processing.R)
+
+Now Processing.R is still in early development stage, not production ready. Welcome to report bugs to [issues](https://github.com/gaocegege/Processing.R/issues)!
 
 ## Installation
 
@@ -19,4 +21,4 @@ See [the documentation about the installation](./docs/howto.md).
 
 ## Useful Resources for Development
 
-See [references](./docs/references.md).
+See [references](./docs/references.md).