Update radio-settings.md

- corrected dBM into dBm
- specified ERP reference
- added link to ERP in-depth article

docs/radio-settings.md

@@ -8,7 +8,7 @@ See [this site](https://www.rfwireless-world.com/Tutorials/LoRa-channels-list.ht
 
 ## LoRaWAN Europe Frequency Band
 
-The maximum power allowed is +14dBM.
+The maximum power allowed is +14dBm ERP (Effective Radiated Power, see [this site](https://en.wikipedia.org/wiki/Effective_radiated_power) for more information).
 
 ### 433 MHz
 
@@ -27,4 +27,4 @@ LoRaWAN defines 64, 125 kHz channels from 902.3 to 914.9 MHz increments.
 The maximum output power for North America is +30 dBM.
 
 The band is from 902 to 928 MHz. It mentions channel number and its respective channel frequency. All the 13 channels are separated by 2.16 MHz with respect to the adjacent channels.  
-Channel zero starts at 903.08 MHz center frequency.
+Channel zero starts at 903.08 MHz center frequency.