How to choose voltage divider resistors for correct biasing in emitter follower circuit?
The current drawn by the base is dependent on the transistor parameter hfe (which varies greatly from one part to another of the same type, and also with temoerature etc). The base current will be the emitter current (emitter voltage divided by Re) divided by the hfe. 

The source (Thevenin equivalent) resistance looking into the divider is R1||R2. 

So they are saying that the voltage drop at the base due to the base current should be small in relation to the supply voltage. That way, hfe can vary over a wide range with little effect on the bias.

A typical choice is a factor of 10, so if hfe is 200 and Re is 1K you would like R1||R2 &lt; 20K.