Merge pull request twbs#15369 from bastienmoulia/woff2

Add woff2 font in readme.md

Author: cvrebert

README.md

@@ -51,7 +51,8 @@ bootstrap/
     ├── glyphicons-halflings-regular.eot
     ├── glyphicons-halflings-regular.svg
     ├── glyphicons-halflings-regular.ttf
-    └── glyphicons-halflings-regular.woff
+    ├── glyphicons-halflings-regular.woff
+    └── glyphicons-halflings-regular.woff2
 ```
 
 We provide compiled CSS and JS (`bootstrap.*`), as well as compiled and minified CSS and JS (`bootstrap.min.*`). CSS [source maps](https://developers.google.com/chrome-developer-tools/docs/css-preprocessors) (`bootstrap.*.map`) are available for use with certain browsers' developer tools. Fonts from Glyphicons are included, as is the optional Bootstrap theme.