Write a table of contents at the beginning of each section

[Aurelie-Mutschler]

Write a table of contents at the beginning of each section

Indicative due date : July 10th, 2017

Criteria to close the issue :

• Update each section page of the prototyping gitbook (https://echopen.gitbooks.io/echopen_prototyping/)
• To edit the gitbook, fork the repo : https://github.com/echopen/echopen_prototyping
• Edit the corresponding markdown file : introduction/new_introduction.md
• Make a pull request refering to this issue

[Aurelie-Mutschler]

thanks @ApollineF