Add 'Linux IP Stacks Commentary - Web Edition' (#7110)

* Add 'Linux IP Stacks Commentary - Web Edition'

* Add annotation to indicate that the web edition is a work-in-progress

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

books/free-programming-books-subjects.md

@@ -610,6 +610,7 @@ Books that cover a specific programming language can be found in the  [BY PROGRA
 * [IPv6 for IPv4 Experts](https://sites.google.com/site/yartikhiy/home/ipv6book) - Yar Tikhiy (PDF)
 * [Kafka gentle introduction](https://www.gentlydownthe.stream) - Mitch Seymour
 * [Kafka, The definitive Guide](https://assets.confluent.io/m/1b509accf21490f0/original/20170707-EB-Confluent_Kafka_Definitive-Guide_Complete.pdf) - Neha Narkhede (PDF)
+* [Linux IP Stacks Commentary](https://www.satchell.net/ipstacks/) - Stephen Satchell, H. B. J. Clifford (HTML) *(:construction: in process)*
 * [Network Science](http://networksciencebook.com) - Albert-Laszló Barabási
 * [Securing Wireless Networks for the Home User Guide](https://mohamedation.github.io/securing-wifi/index-en.html) - Mohamed Adel (HTML)
 * [The TCP/IP Guide](http://www.tcpipguide.com/free/t_toc.htm)