sv_cheats 1; ent_create game_text targetname hi message "MESSAGE GOES HERE" channel 1 color "255 255 255" color2 "255 255 255" holdtime 5 x -1 y -1 spawnflags 1; ent_fire hi display; sv_cheats 0

(Will only work if cheats are enabled)

Replace MESSAGE GOES HERE with whatever you want

Channel 1 changes the channel of the message, there's 4 channels, each one can only show one message at a time, use different channels if multiple people are using this trick

Color is self explanatory, play around with the RGB value

Holdtime changes how long the message is shown, change the 5 to how many seconds you want

x -1, and y -1 changes where the message will be displayed on the screen, -1 on both centers it