Add documentation for the llfs api

docs/llfs.md

@@ -0,0 +1,57 @@
+# LLFS (Linked List File System)
+
+## Introduction
+The llfs filesystem can be generated using the mkllfss utility. 
+It is a simple filesystem that uses a linked list to store files. 
+The filesystem is stored in a single c file (`llfs_data.c`), which can be compiled and read by the llfs library.
+The llfs filesystem is a flat filesystem, meaning that it does not support directories.
+
+## Usage of the llfs API
+### Getting a list of files
+```c
+#include "llfs.h"
+
+void main(void) {
+    // Allocate space for 10 files
+    llfs_file_t file_list[10];
+    
+    // Get the file list
+    size_t file_count = llfs_file_list(file_list, 10, NULL);
+    
+    // Loop through the files and print their names and sizes
+    for (int i = 0; i < file_count; i++) {
+        LOG_INFO(TAG, "File: %s, size: %d", file_list[i].name, file_list[i].len);
+    }
+}
+```
+Result:
+```
+[Info]      (2009) [main]: File: image.bmp, size: 9270
+[Info]      (2013) [main]: File: python_file.py, size: 645
+[Info]      (2019) [main]: File: image2.bmp, size: 7738
+[Info]      (2024) [main]: File: filename with a space.txt, size: 61
+[Info]      (2031) [main]: File: file1.txt, size: 77
+```
+
+### Reading a file
+```c
+#include "llfs.h"
+
+void main(void) {
+    // Get a file by name
+    llfs_file_t *file = llfs_file_open("filename with a space.txt");
+    
+    if (file != NULL) {
+        // Print the file name, size and data
+        LOG_INFO(TAG, "File found: %s, size: %d", file->name, file->len);
+        LOG_INFO(TAG, "File data: %s", file->data);
+    } else {
+        LOG_WARN(TAG, "File not found");
+    }
+}
+```
+Result:
+```
+[Info]      (2040) [main]: File found: filename with a space.txt, size: 61
+[Info]      (2047) [main]: File data: This is a file with a space in it's filename.
+```