Update .Net Url (EbookFoundation#6673)

* Update .Net Url

As the previose was 404 not found

* Add crosslink ref to C# section on .Net section

* Update free-courses-en.md

* fix: adopt linter 1-0-2 rule

Thats is, 2 empty lines between headings / sections

Co-authored-by: David Ordás <[email protected]>

Author: MahmoudHamdy00

courses/free-courses-en.md

@@ -750,7 +750,7 @@
 
 ### .NET
 
-* [Learn how to program: .NET](https://www.learnhowtoprogram.com/net) - Epicodus Inc.
+> :information_source: See also … [C#](#c-sharp)
 
 
 ### Objective-C