add nand2tetris (#6239)

* add nand2tetris

* fix formatting for nand2tetris

courses/free-courses-en.md

@@ -895,6 +895,7 @@
 
 ### Verilog / VHDL / SystemVerilog
 
+* [nand2tetris](https://www.nand2tetris.org) - Shimon Schocken, Noam Nisan (Coursera)
 * [SOC Verification Using SystemVerilog](http://verificationexcellence.in/online-courses/soc-verification-using-systemverilog)
 * [SystemVerilog - Learn basics of SystemVerilog for Hardware Verification](https://verificationexcellence.teachable.com/p/learn-systemverilog)
 * [SystemVerilog based UVM Methodology - Learn to build UVM based Testbenches in SystemVerilog](https://verificationexcellence.teachable.com/p/learn-ovm-uvm)