Add cross-link to awesome-europe

[GeiserX]

Hi! awesome-europe is a curated list of 558+ open source projects for the European Union and EEA. It includes 30+ transport and mobility entries (HAFAS, NeTEx, ETCS, SIRI, Transitous, OpenTripPlanner EU deployments, etc.) that complement this list. Would you consider adding a cross-link in a 'Related lists' or 'See also' section? Happy to submit a PR if preferred!