What is the simplest circuit to measure RELATIVE RF signal strength with multimeter?
A schottky diode rectifier, the circuit you've posted, is the simplest way to read RF on a multimeter. Build it and see if it works for your power level and frequency, you may be OK. 

You would connect the two inputs labelled GND and RF to the two outputs of the dipole. Note that GND is just a label, it doesn't need to be connected to earth, it really means 'the terminal against which the RF signal is measured'.

Read the output voltage without RF present. Any change from that means an RF input, and a larger change means a larger signal.

However, there are two issues.

a) The signal has to be 'big' enough. A simple unbiased diode is quite insensitive for small signals. Biassing it so that it always conducts a trickle of current, and then measuring the change of output voltage with RF, makes it more sensitive. For instance, connecting the +VE output terminal through 100k to -1.5v (a single AA for instance) with respect to ground would pull an adequate biassing current through the diode. 

Rather than simply measure the output voltage, which will be sensitive to temperature and bias current, it's a good idea to have two identically biassed diodes, only one fed with RF, and measure the difference between the two outputs. The offset voltage on the reference diode will track changes due to temperature and bias current on the detector diode, making the measurement more stable.

b) The diode has to be 'fast' enough for the frequency you are detecting. Although schottky diodes are inherently very fast, as in they don't have the carrier storage times associated with junction didoes, they still have junction capacitance and package inductance, which attenuate the RF at higher frequencies. You can get diodes in surface mount packages, to reduce inductance. You can get microwave diodes, with much lower junction capacitance.