Translation

Added a guide on how to include the language switch in a jupyter-book as part of the additional information of the manual

content/additional/transaltion_guide.md

+## HOW TO CREATE A BOOK WITH TRANSLATION
+
+
+Organize your book with the following folders tree:
+
+	├── book_EN
+	|	├── _static
+	|	|	├── img
+	|	|	|	├── nl.png
+	|	|	|	└── en.png
+	|	|	|
+	|	|	└── translation.js
+	|	|
+	|	├── _config.yml
+	|	├── _toc.yml
+	|	└── other files/folders ....		
+	|	
+	└──	book_NL
+		├── _static
+		|	├── img
+		|	|	├── nl.png
+		|	|	└── en.png
+		|	|
+		|	└── translation.js
+		|
+		├── _config.yml
+		├── _toc.yml
+		└── other files/folders ...	
+	
+and make sure that the `_static` folder is the same in the two book folders (`book_EN` and `book_NL`).
+
+**You can find the content of the `_static` folder in this [repository](https://gitlab.tudelft.nl/opentextbooks/language-switch)**
+
+Navigate to the `book_EN` folder and build the book.
+If you don't have python installed make sure to activate the virtual environment.
+
+```bash
+cd <path>/book_EN
+jupyter-book build .
+```
+
+Navigate to the `book_NL` folder and build that book too.
+
+```bash
+cd ../book_NL
+jupyter-book build .
+```
+
+at this point the folder tree should look like this
+
+	├── book_EN
+	|	├── _build
+	|	|	├── .doctrees
+	|	|	└── html		
+	|	|
+	|	├── _static
+	|	|	├── img
+	|	|	|	├── nl.png
+	|	|	|	└── en.png
+	|	|	|
+	|	|	└── translation.js
+	|	|
+	|	├── _config.yml
+	|	├── _toc.yml
+	|	└── other files/folders ....		
+	|	
+	└──	book_NL
+		├── _build
+		|	├── .doctrees
+		|	└── html		
+		|
+		├── _static
+		|	├── img
+		|	|	├── nl.png
+		|	|	└── en.png
+		|	|
+		|	└── translation.js
+		|
+		├── _config.yml
+		├── _toc.yml
+		└── other files/folders ...	
+		
+rename the `html` folder of the dutch book to `nl`.
+Assuming you are still in the `book_NL` from the building command
+
+```bash
+cd _build
+mv html nl
+```
+
+move the renamed folder inside the html folder of the english book
+
+```bash
+cp -r nl ../../book_EN/_build/html
+```
+
+browse the jupyter book with 2 languages at
+
+	└── book_EN
+		└── _build
+			└── html
+				└── index.html