Add documentation.

apps/README.md

@@ -5,4 +5,6 @@ These are sample applications with various purposes.
 - [ADC DMA Chain](/apps/adc_dma_chain): Chained DMA data acquisition from the ADC.
 - [Barometer](/apps/barometer): Barometer polling the temperature and atmospheric pressure from a BMP180.
 - [Iperf Server](/apps/iperf_server): A tool to measure the performance of the TinyUSB's TCP/IP stack over USB.
-- [TCP Server](/apps/tcp_server): A TCP server example to send high-frequency data to the host computer.
+- [TCP Server](/apps/tcp_server): A TCP server example to send high-frequency data to the host computer.
+- [Filesystem](/apps/filesystem): A simple non-volatile filesystem based on LittleFS. It uses the internal flash.
+- [Altimeter](/apps/filesystem): A simple altimeter for rockets, kites, balloons, etc.

apps/altimeter/README.md

@@ -0,0 +1,6 @@
+# Filesystem
+This is a simple altimeter based on LittleFS and BMP390. This is using the built-in Raspberry Pi Pico as non-volatile memory.
+
+### Dependencies
+- [littlefs](/lib/littlefs) Library.
+- [bmp390](/lib/bmp390) Library.

apps/filesystem/README.md

@@ -0,0 +1,5 @@
+# Filesystem
+This is a simple filesystem demonstration based on LittleFS. This is using the built-in Raspberry Pi Pico as non-volatile memory.
+
+### Dependencies
+- [littlefs](/lib/littlefs) Library.

lib/littlefs/README.md

@@ -0,0 +1,2 @@
+# LittleFS Library
+This is a library implements the LittleFS driver for the built-in Raspberry Pi Pico flash storage.