Add more social profiles

[mkurz]

• https://www.twitch.tv/playframework
• https://www.youtube.com/channel/UCRp6QDm5SDjbIuisUpxV9cg
  • https://www.youtube.com/PlayFramework is taken already :(
• https://www.linkedin.com/groups/3818467/ (I am admin of this group now)