jupyter_notebook_en.ipynb: Some updates

[MMesgar]

Update the following:
Task2: --> Can we add a link to the "colab's markdown guide"?
Task 3 --> print("hello world") should be in Python print("hello world")

Add the following:
Some tasks from the ... should be transferred to this file as well.

1. By using the Insert -> Insert Cell Above / Below option new cells can be inserted above and below this cell. The cell type can be changed using the drop-down menu. By default a cell is a code cell after creation. (Keyboard Shortcut: Click on a cell, and then press "a" to create a cell above it, or press "b" to create a cell below it.)* To delete a cell, simply select the corresponding cell and remove it via Edit -> Delete Cells. (Keyboard Shortcut: Click on the cell, then press "d" twice.) *Create a new code and markdown cell.

2. Variables / functions / imported libraries of a code cell can be accessed in all subsequent code cells. The output of a code cell can be deleted via Cell -> Current Outputs -> Clear. If you want to delete the output of all cells, you can do this via Cell -> All Output -> Clear.* Try the following on the two code cells Cell 1 and Cell 2: 1. Execute Cell 1 and Cell 2 one after the other. 2. Change the value of "variable" to 16 and then execute Cell 2. 3. Change the value of "variable" to 17 and execute Cell 1 and Cell 2 one after the other.

3. variable in once cell and print variable in another cell.