Update SVD README.md (#165)

Author: carlynorama

Tools/SVDs/README.md

@@ -1,5 +1,12 @@
 # SVDs
 
+`SVD` stands for System View Description and they are an `XML` schema created by ARM to represent the [CMSIS](https://www.arm.com/technologies/cmsis) information typically for Arm Cortex-M microcontrollers. They can be used for generating headers and providing information to debuggers among other tasks. `CMSIS` stands for _Common Microcontroller Software Interface Standard_ and was created as a hardware abstraction layer to be independent of what silicon vendor was implementing the ARM standard. 
+
+More information:
+- https://arm-software.github.io/CMSIS_6/latest/General/index.html
+- https://open-cmsis-pack.github.io/svd-spec/latest/index.html
+- https://www.arm.com/company/news/2012/02/arm-extends-cmsis-with-rtos-api-and-system-view-description
+
 The SVDs used in this repo have been copied from the following sources.
 
 | file                 | source                                                               |