Document p2p_disabled option in wpa_supplicant.conf

I needed this option to disable P2P on a buggy system.
Document this so someone else finds it quicker next time.

Signed-off-by: Ben Greear <greearb@candelatech.com>

wpa_supplicant/wpa_supplicant.conf

@@ -297,6 +297,10 @@ fast_reauth=1
 # format: <backend name>[:<optional backend parameters>]
 #ext_password_backend=test:pw1=password|pw2=testing
 
+
+# Disable P2P functionality
+# p2p_disabled=1
+
 # Timeout in seconds to detect STA inactivity (default: 300 seconds)
 #
 # This timeout value is used in P2P GO mode to clean up