Fix functions in docs: RP2040 Helper Class (#793)

Author: NuclearPhoenixx

docs/rp2040.rst

@@ -33,8 +33,8 @@ values returned may not meet the most stringent random tests.  **If your
 application needs absolute bulletproof random numbers, consider using
 dedicated external hardware.**
 
-void reboot()
-~~~~~~~~~~~~~
+void rp2040.reboot()
+~~~~~~~~~~~~~~~~~~~~
 Forces a hardware reboot of the Pico.
 
 Memory Information
@@ -47,8 +47,8 @@ that because there is some overhead, and there may be heap fragmentation,
 this number is an *upper bound* and you generally will only be able to allocate
 less than this returned number.
 
-int rp2040.getUsedHeap
-~~~~~~~~~~~~~~~~~~~~~~
+int rp2040.getUsedHeap()
+~~~~~~~~~~~~~~~~~~~~~~~~
 Returns the number of bytes allocated out of the heap.
 
 int rp2040.getTotalHeap()