Update README.md

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

README.md

@@ -1,6 +1,4 @@
-# STM32SD
-
-## SD library for Arduino
+# STM32 SD library for Arduino
 
 With an STM32 board with SD card slot availability, this library enables
 reading and writing on SD card using SD card slot of a STM32 board (NUCLEO, DISCOVERY, ...).
@@ -10,9 +8,16 @@ This library follow Arduino API.
 For more information about it, please visit:
 http://www.arduino.cc/en/Reference/SD
 
-## Note
+## Dependency
 
-The library is based on FatFs, a generic FAT file system module for small embedded systems.  
+This library is based on FatFs, a generic FAT file system module for small embedded systems.  
 [http://elm-chan.org/fsw/ff](http://elm-chan.org/fsw/ff/00index_e.html)
 
 The FatFs has been ported as Arduino library [here](https://github.com/stm32duino/FatFs). The STM32SD library depends on it.
+
+## Configuration
+The FatFs has several user defined options, which is specified from within the `ffconf.h` file.
+
+This library provides a default user defined options file named `ffconf_default.h`.
+
+User can provide his own defined options by adding his configuration in a file named `ffconf_custom.h` at sketch level or in variant folder.