Add several Scaler Topics tutorials (EbookFoundation#6959)

* Added a useful resource

Have added a useful resource about the Bootstrap from the Scaler topics in the Bootstrap section.

* Update free-programming-interactive-tutorials-en.md

* Update free-programming-interactive-tutorials-en.md

* fix: spaces between link markup tokens

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

Author: Vaishnavi Amira Yada

more/free-programming-interactive-tutorials-en.md

@@ -67,6 +67,7 @@
 
 ### C
 
+* [C Tutorial](https://www.scaler.com/topics/c/) - Scaler Topics
 * [Learn C](http://www.learn-c.org) - Learn-C
 
 
@@ -82,6 +83,7 @@
 ### <a id="cpp"></a>C++
 
 * [C++ Tutorial](https://www.w3schools.com/cpp) - W3Schools
+* [C++ Tutorial](https://www.scaler.com/topics/cpp/) - Scaler Topics
 * [CppKoans](https://github.com/torbjoernk/CppKoans)
 
 
@@ -167,6 +169,7 @@
 * [Grid Attack](https://codingfantasy.com/games/css-grid-attack) - Nick Bull
 * [Grid Garden](https://cssgridgarden.com)
 * [HTML Tutorial](https://www.w3schools.com/html/) - W3Schools
+* [HTML Tutorial](https://www.scaler.com/topics/html/) - Scaler Topics
 * [Knights of the Flexbox Table](https://knightsoftheflexboxtable.com)
 * [Learn by doing beginner projects](https://dash.generalassemb.ly)
 * [Learn CSS: an evergreen CSS course and reference to level up your styling expertise](https://web.dev/learn/css/) - Andy Bell, Rachel Andrew, Una Kravets, Adam Argyle, Rob Dodson, Jiwoong Lee et al. (web.dev)
@@ -187,6 +190,7 @@
 * [CodingBat code practice](http://codingbat.com/java)
 * [Java at Codecademy](https://www.codecademy.com/courses/learn-java)
 * [Java Tutorial](https://www.w3schools.com/java) - W3Schools
+* [Java Tutorial](https://www.scaler.com/topics/java/) - Scaler Topics
 * [Learn Java](http://www.learnjavaonline.org)
 * [Learneroo Java tutorial](https://www.learneroo.com/modules/11)
 
@@ -201,6 +205,7 @@
 * [Javascript interactive tutorial on CodeCademy](https://www.codecademy.com/learn/javascript)
 * [JavaScript interactive tutorial on CoderMania](http://www.codermania.com/javascript/lesson/1a/hello-world)
 * [JavaScript Tutorial](https://www.w3schools.com/js) - W3Schools
+* [JavaScript Tutorial](https://www.scaler.com/topics/javascript/) - Scaler Topics
 * [Javascripting](https://github.com/sethvincent/javascripting)
 * [Learn JavaScript](http://www.learn-js.org)
 * [Learn knockout.js](http://learn.knockoutjs.com)
@@ -256,6 +261,7 @@
 #### Operating systems
 
 * [Learning operating system development using Linux kernel and Raspberry Pi](https://github.com/s-matyukevich/raspberry-pi-os) - Sergey Matyukevich (:construction: *in process*)
+* [Operating System Tutorial](https://www.scaler.com/topics/operating-system/) - Scaler Topics
 * [Project eXpOS: eXperimental Operating System](https://exposnitc.github.io) - Dr. Murali Krishnan K., Department of Computer Science and Engineering of the Calicut National Institute of Technology (HTML)
 
 
@@ -323,6 +329,7 @@
 * [Python Programming Language](https://www.geeksforgeeks.org/python-programming-language/) - GeeksforGeeks
 * [Python Tutorial](https://www.tutlane.com/tutorial/python) - tutlane
 * [Python Tutorial](https://www.w3schools.com/python) - W3Schools
+* [Python Tutorial](https://www.scaler.com/topics/python/) - Scaler Topics
 * [Scientific Computing with Python Certification](https://www.freecodecamp.org/learn/scientific-computing-with-python/) - freeCodeCamp
 
 
@@ -375,6 +382,7 @@
 * [SQL Server Tutorial](https://www.tutlane.com/tutorial/sql-server) - tutlane
 * [SQL Teaching](https://www.sqlteaching.com)
 * [SQL Tutorial](https://www.w3schools.com/sql) - W3Schools
+* [SQL Tutorial](https://www.scaler.com/topics/sql/) - Scaler Topics
 * [SQLBolt](http://sqlbolt.com)