The data below is based on season 3 data (season 4 is too new), and the maximum (not current) skill rating of the player during the season. The values below are also rounded, so that's why it doesn't quite add up to 100%.
Bronze - 6%
Silver - 22%
Gold - 34%
Platinum - 23%
Diamond - 10%
Master - 3%
Grandmaster - <1%
Some interesting notes:
Median maximum skill rating is not 2500, it's actually a little above 2300. So if you have a maximum skill rating of 2350, you have a higher SR than 50% of the population!
If you do a breakdown based upon the more volatile current skill rating, there's even fewer players above 3000 SR than listed above. Only around 8% of the population was above 3000 SR for season 3 at any one time.