Update rp2040.rst (#1704)

isPicoW was missing the rp2040. qualifier.

Author: wd5gnr

docs/rp2040.rst

@@ -81,8 +81,8 @@ overhead).
 Hardware Identification
 -----------------------
 
-bool isPicoW()
-~~~~~~~~~~~~~~
+bool rp2040.isPicoW()
+~~~~~~~~~~~~~~~~~~~~~
 Returns the core's best guess if this code is running on a Raspberry Pi Pico W.
 This would let you, possibly, use the same UF2 for Pico and PicoW by simply not
 doing any WiFi calls.