Add medium, youtube, github, twitter icon and links

[takahirom]

Overview (Required)

• you can use that icon from 2018

                      "https://twitter.com/droidkaigi"
                      "https://github.com/DroidKaigi/conference-app-2018"
                      "https://www.youtube.com/channel/UCgK6L-PKx2OZBuhrQ6mmQZw"
                      "https://medium.com/droidkaigi"

Links

• https://github.com/DroidKaigi/conference-app-2018

[henteko]

これやります！

[takahirom]

Thanks 👍 Assigned