Add journal

module2/exo4/example.md

+# Example of Hydrogen Usage
+
+```kotlin
+println("Hello World!") // I use the kotlin kernel
+```
+
+Kotlin allow to `html` outputs:
+```kotlin
+HTML("<h1>This is the Header !</h1>")
+```
+
+```python
+print('Hello World!') # I use the python kernel
+```
+
+You can also use pyplot or graphical ouputs :
+```python
+import matplotlib.pyplot as plt
+
+%matplotlib inline
+plt.plot([2, 3, 4, 5])
+plt.show()
+```
+
+```bash
+hostname
+```

module2/exo4/journal.md

+# Hydrogen : An alternative to Jupyter
+
+## Installation
+
+[Hydrogen](https://nteract.io/) is an extension for [Atom](https://atom.io/) editor. It works with [Jupyter](https://jupyter.org/) and multiple languages.
+
+To install atom use the link above to download atom. I recommand to use conda to install python and jupyter. Install the last nodejs version from [here](https://nodejs.org/en/).
+
+Once you have installed Jupyter, Node and Atom you can install hydrogen :
+
+```bash
+apm install hydrogen
+```
+
+## Usage
+
+For each language you have to install the grammar in Atom and the kernel in Jupyter. For the most common languages it's generally easy to find both.
+
+### Example
+
+To install allow Hydrogen to handle the Kotlin language, I search `language kotlin` in the package manager of atom (menu `Edit > Preferences > Install`).
+
+I found this one [atom-kotlin-language](https://github.com/alexmt/atom-kotlin-language). You must verify that the package contains the language grammar. If you know the package name you can install it with apm (Atom package manager) :
+
+```bash
+apm install language-kotlin
+```
+
+After that I install the kotlin kernel available on [github](https://github.com/Kotlin/kotlin-jupyter):
+
+```bash
+conda install kotlin-jupyter-kernel -c jetbrains
+```
+
+When the both tasks are done you can know execute the code in block comments by pressing `Ctrl + Enter` in the block section :
+
+```python
+print("Hello World")
+```
+
+```markdown
+​```kotlin
+println("Hello World")
+​```
+```
+
+![Kotlin run example](run_kt.png)
+
+You can use multiple languages in the same document, as the kernel is choose by the language name, i.e. the code block :
+
+```markdown
+ This block will call python interpreter
+​ ```python
+ print('ok')
+ ```
+ This block will call kotlin interpreter
+ ```kotlin
+ println("Ok")
+ ```
+```
+
+You can find an usage example at [usage](example.md) and view the [result in the IDE](example.png)