Updates to comments and README.md to add new target links

Author: sg-

README.md

@@ -37,6 +37,7 @@ NXP:
 Freescale:
 * [KL25Z](http://mbed.org/platforms/KL25Z/) (Cortex-M0+)
 * KL05Z (Cortex-M0+)
+* [KL46Z](https://mbed.org/platforms/FRDM-KL46/) (Cortex-M0+)
 
 STMicroelectronics:
 * STM32F407 (Cortex-M4)

libraries/mbed/targets/hal/TARGET_Freescale/TARGET_KL46Z/PinNames.h

@@ -231,7 +231,7 @@ typedef enum {
     NC = (int)0xFFFFFFFF
 } PinName;
 
-/* PullDown not available for KL46 */
+/* Pull modes for input pins */
 typedef enum {
     PullNone = 0,
     PullDown = 2,