chore: Add gitter link

Author: Stranger6667

README.md

@@ -3,6 +3,7 @@
 [![ci](https://github.com/Stranger6667/css-inline/workflows/ci/badge.svg)](https://github.com/Stranger6667/css-inline/actions)
 [![Crates.io](https://img.shields.io/crates/v/css-inline.svg)](https://crates.io/crates/css-inline)
 [![docs.rs](https://docs.rs/css-inline/badge.svg?version=0.5.0)](https://docs.rs/css-inline/0.5.0/css_inline/)
+[![gitter](https://img.shields.io/gitter/room/Stranger6667/css-inline.svg)](https://gitter.im/Stranger6667/css-inline)
 
 A crate for inlining CSS into HTML documents. When you send HTML emails, you need to use "style" attributes instead of "style" tags.
 
@@ -121,3 +122,7 @@ OPTIONS:
     --extra-css
         Additional CSS to inline.
 ```
+
+## Support
+
+If you have anything to discuss regarding this library, please, join our [gitter](https://gitter.im/Stranger6667/css-inline)!