Added links to ramcrc32bd and ramrsbd

These two small libraries provide examples of error-correction that is
compatible with littlefs (or any filesystem really).

It would be nice to eventually provide these as drop-in solutions, but
right now it's not really possible without breaking changes to
littlefs's block device API.

In the meantime ramcrc32bd and ramrsbd at least provide example
implementations that can be adapted to users' own block devices.

README.md

@@ -251,6 +251,12 @@ License Identifiers that are here available: http://spdx.org/licenses/
   filesystem over USB. Allows mounting littlefs on a host PC without additional
   drivers.
 
+- [ramcrc32bd] - An example block device using littlefs's 32-bit CRC for
+  error-correction.
+
+- [ramrsbd] - An example block device using Reed-Solomon codes for
+  error-correction.
+
 - [Mbed OS] - The easiest way to get started with littlefs is to jump into Mbed
   which already has block device drivers for most forms of embedded storage.
   littlefs is available in Mbed OS as the [LittleFileSystem] class.
@@ -281,6 +287,8 @@ License Identifiers that are here available: http://spdx.org/licenses/
 [mklfs]: https://github.com/whitecatboard/Lua-RTOS-ESP32/tree/master/components/mklfs/src
 [mklittlefs]: https://github.com/earlephilhower/mklittlefs
 [pico-littlefs-usb]: https://github.com/oyama/pico-littlefs-usb
+[ramcrc32bd]: https://github.com/geky/ramcrc32bd
+[ramrsbd]: https://github.com/geky/ramrsbd
 [Mbed OS]: https://github.com/armmbed/mbed-os
 [LittleFileSystem]: https://os.mbed.com/docs/mbed-os/latest/apis/littlefilesystem.html
 [SPIFFS]: https://github.com/pellepl/spiffs