[ARM] Add memory.txt to 00-INDEX

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

Documentation/arm/00-INDEX

@@ -16,5 +16,7 @@ empeg
 	- Empeg documentation
 mem_alignment
 	- alignment abort handler documentation
+memory.txt
+	- description of the virtual memory layout
 nwfpe
 	- NWFPE floating point emulator documentation