[docs] Add Porting new families guide

docs/contrib/ota/library.md

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+# uf2ota library
+
+uf2ota library allows to write a LibreTiny UF2 file to the flash, while parsing all the necessary tags. It manages the target partitions, compatibility checks, and works on top of the FAL provided by FlashDB.
+
+## Usage example
+
+```c
+uint8_t target	   = 1;			 // target OTA scheme - 1 or 2
+uint32_t family	   = F_RTL8710B; // chip's UF2 family ID
+uf2_ota_t *ctx	   = uf2_ctx_init(target, family);
+uf2_info_t *info   = uf2_info_init(); // optional, for getting firmware info
+uf2_block_t *block = (uf2_block_t *)malloc(UF2_BLOCK_SIZE);
+uf2_err_t err;
+
+// ... // read the first header block (512 bytes) into *block
+
+// check the block for validity
+err = uf2_check_block(ctx, block);
+if (err > UF2_ERR_IGNORE)
+	// handle the error
+	return;
+
+// parse the header block
+// note: if you don't need info, you can skip this step and call uf2_write() directly
+err = uf2_parse_header(ctx, block, info);
+if (err)
+	// handle the error
+	return;
+
+while (/* have input data */) {
+
+	// ... // read the next block into *block
+
+	// check the block for validity
+	err = uf2_check_block(ctx, block);
+	if (err == UF2_ERR_IGNORE)
+		// skip this block
+		continue;
+	if (err)
+		// handle the error
+		return;
+
+	// write the block to flash
+	err = uf2_write(ctx, block);
+	if (err > UF2_ERR_IGNORE)
+		// handle the error
+		return;
+}
+
+// finish the update process
+
+// ... // activate your new OTA partition
+
+// cleanup
+free(ctx);
+free(block);
+uf2_info_free(info);
+```