Add an explanation about why using robots on your project

[frinyvonnick]

The motivation section explains the advantages of Hygie over having mutiple tools doing the same thing but it doesn't point on a resources that explain the purpose of using robots on your project. There is a nice guide about maintaining open source project have a section dedicated to this subject.

Maybe we could add a sentence that explains briefly how useful it is with a link to this guide for further informations ?