Update CONTRIBUTING.rst

* Fixes minor  typos
installation: github repository url fix

* Fixes GitHub repository url used

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
deposit: addition of metadata extraction in deposit form

* Adds a button in order to extract metadata.

* Runs the extraction tool depending on the doi input.

Signed-off-by: Konstantinos Kostis <konstantinos.kostis@cern.ch>