boards/nucleo144-l4: add pinout source

boards/nucleo-l496zg/doc.txt

@@ -10,7 +10,7 @@ STM32L496ZG ultra-low-pawer microcontroller with 320KiB of RAM and 1 MiB of Flas
 
 ## Pinout
 
-@image html pinouts/nucleo-l496zg.svg "Pinout for the nucleo-l496zg (from STM board manual)" width=55%
+@image html pinouts/nucleo-l496zg.svg "Pinout for the Nucleo-L496ZG (from STM user manual, UM2179, https://www.st.com/resource/en/user_manual/um2179-stm32-nucleo144-boards-mb1312-stmicroelectronics.pdf, page 31)" width=55%
 
 ### MCU
 

boards/nucleo-l4r5zi/doc.txt

@@ -14,7 +14,7 @@ STM32L4R5ZI microcontroller with 640KiB of RAM and 2MiB of ROM Flash.
 
 ## Pinout
 
-@image html pinouts/nucleo-l4r5zi.svg "Pinout for the nucleo-l4r5zi (from STM board manual)" width=55%
+@image html pinouts/nucleo-l4r5zi.svg "Pinout for the Nucleo-L4R5ZI (from STM user manual, UM2179, http://www.st.com/st-web-ui/static/active/en/resource/technical/document/user_manual/um2179-stm32-nucleo144-boards-mb1312-stmicroelectronics.pdf, page 35)" width=55%
 
 ### MCU
 
@@ -36,7 +36,7 @@ STM32L4R5ZI microcontroller with 640KiB of RAM and 2MiB of ROM Flash.
 | Datasheet    | [Datasheet](https://www.st.com/resource/en/datasheet/stm32l4r5zi.pdf)|
 | Reference Manual | [Reference Manual](https://www.st.com/resource/en/reference_manual/rm0432-stm32l4-series-advanced-armbased-32bit-mcus-stmicroelectronics.pdf)|
 | Programming Manual | [Programming Manual](https://www.st.com/resource/en/programming_manual/pm0214-stm32-cortexm4-mcus-and-mpus-programming-manual-stmicroelectronics.pdf)|
-| Board Manual | [Board Manual](http://www.st.com/st-web-ui/static/active/en/resource/technical/document/user_manual/um2179-stm32-nucleo144-boards-mb1312-stmicroelectronics-1.pdf)|
+| Board Manual | [Board Manual](http://www.st.com/st-web-ui/static/active/en/resource/technical/document/user_manual/um2179-stm32-nucleo144-boards-mb1312-stmicroelectronics.pdf)|
 
 ## Flashing the device