Update free-courses-en.md (#4539)

free-courses-en.md

@@ -5,6 +5,7 @@
 * [Angular](#angular)
 * [Assembly](#assembly)
 * [Bash / Shell](#bash--shell)
+* [Bootstrap](#bootstrap)
 * [C](#c)
 * [C#](#c-sharp)
 * [C++](#c-1)
@@ -115,6 +116,11 @@
 * [Shell Scripting Tutorial](https://www.youtube.com/playlist?list=PL7B7FA4E693D8E790)
 
 
+### Bootstrap
+
+* [Rapid website design with Bootstrap](https://www.udemy.com/course/responsive-website-design) - Laurence Svekis (Udemy)
+
+
 ### C
 
 * [C Programming Tutorial](https://www.youtube.com/playlist?list=PL_RGaFnxSHWoGzOXqtKeM71OLpvZbuU0P)