doc: update README.md

add link to source as they are now available on GitHub.

Signed-off-by: Frederic Pillon <[email protected]>

Author: fpistm

README.md

@@ -5,7 +5,6 @@ FatFs has being developped as a personal project of the author, ChaN.
 
 See [elm-chan.org/fsw/ff](http://elm-chan.org/fsw/ff/00index_e.html)
 
-Modified by ST, see the st_readme.txt.
-Modified to fit Arduino libraries specifications.
+Modified by ST, used source from [stm32_mw_fatfs](https://github.com/STMicroelectronics/stm32_mw_fatfs) and modified to fit Arduino libraries specifications.
 
-It is used by the STM32SD library.
+It is used by the [STM32SD](https://github.com/stm32duino/STM32SD) library.