Merge pull request #674 from theamirocohen/FS_thread_safe

Updating file system thread safe ability

Author: Amanda Butler

docs/reference/api/storage/FATFileSystem.md

@@ -20,6 +20,8 @@ The first step to using the FAT file system is formatting storage with FAT. You
 
 The FAT file system supports external flash; however, it must allocate a full erase block for internal operations, which can become large for some forms of flash. If RAM consumption becomes a problem, we suggest switching to LittleFileSystem. The Mbed OS file system APIs make switching file systems a straightforward task. One common strategy is to use the FAT file system for debugging and switch to LittleFileSystem when the application becomes stable.
 
+The FAT file system is thread safe. Although the FAT file system is built on the ChanFS project, synchronizing in the C++ layer allows you to use the C++ RTOS APIs directly.
+
 ### Usage
 
 Instantiate the `FATFileSystem` class with a block device and file path.

docs/reference/api/storage/LittleFileSystem.md

@@ -29,6 +29,8 @@ We built this for microcontrollers with external flash storage. In this context,
 
 For storage on an SD card that is accessible from a PC, use the FATFileSystem due to its portability.
 
+LittleFileSystem is thread safe.
+
 ### Usage
 
 Instantiate the `LittleFileSystem` class with a block device and file path.