reorganize files (#5199)

* reorganize files

1. make it easier to find files
2. reduce scrolling to get to README on main view of repo

* remove tr.txt again

books/free-programming-books-nl.md

@@ -0,0 +1,51 @@
+### Index
+
+* [C](#c)
+* [C#](#c-sharp)
+* [COBOL](#cobol)
+* [Java](#java)
+* [PHP](#php)
+  * [Symfony](#symfony)
+* [Python](#python)
+* [Scratch](#scratch)
+
+
+### C
+
+* [Programmeren in C](https://nl.wikibooks.org/wiki/Programmeren_in_C) - Wikibooks
+
+
+### C Sharp
+
+* [Programmeren in C Sharp](https://nl.wikibooks.org/wiki/Programmeren_in_C_Sharp) - Wikibooks
+
+
+### COBOL
+
+* [Programmeren in COBOL](https://nl.wikibooks.org/wiki/Programmeren_in_COBOL) - Wikibooks
+
+
+### Java
+
+* [Programmeren in Java](https://nl.wikibooks.org/wiki/Programmeren_in_Java) - Wikibooks
+
+
+### PHP
+
+* [Programmeren in PHP](https://nl.wikibooks.org/wiki/Programmeren_in_PHP) - Wikibooks
+
+
+#### Symfony
+
+* [Symfony 5: Snel van start](https://symfony.com/doc/current/the-fast-track/nl/index.html)
+
+
+### Python
+
+* [De Programmeursleerling: Leren coderen met Python 3](http://www.spronck.net/pythonbook/dutchindex.xhtml) - Pieter Spronck (PDF) (3.x)
+* [Programmeren in Python](https://nl.wikibooks.org/wiki/Programmeren_in_Python) - Wikibooks
+
+
+### Scratch
+
+* [Creatief Computergebruik](http://scratched.gse.harvard.edu/resources/creatief-computergebruik)