If you want to be easy accessible on Steam, you need to set up a custom URL. This is quite easy and can be done on your profile page here: https://steamcommunity.com/id/me/edit.
After that, use the name you enter for your custom URL as your username. Now people can go straight to your profile and add you as a friend.
Tom Clancy's Rainbow Six Siege is a first-person tactical shooter, in which players take control of an operator from the Rainbow team, a counter-terrorist unit. Different operators have different nationalities, weapons, bombs and gadgets. The game features an asymmetrical structure whereby the teams are not always balanced in their ability choices. The Counter Terrorism Units (CTUs) available for play include FBI's Hostage Rescue Team, the British SAS, Germany's GSG-9, Russian Spetsnaz and France's GIGN, each of which has four operators per CTU. Canadian operators from Joint Task Force 2, two American operators from the US Navy SEALs, two Brazilian operators from BOPE as well as two Japanese SAT operators have been added in recent updates.