Hi Lyes
Contact me privately gs@smytheDOTco,za and/or contribute here: GSIP-237 Update OpenAPI (Swagger) specs and/or in the Wiki: GSIP 237 · geoserver/geoserver Wiki · GitHub (ask for Wiki editor access).
Like Andrea says, if you have small improvements that you want to contribute right now (e.g. because a spelling mistake is bugging you), then see Quickfix — GeoServer 3.0 Documentation Guide
Peter