README.md: add BMP, TGA

+ nothings/stb attribution

Author: MartinPulec

README.md

@@ -58,7 +58,8 @@ Features
 - support for _color transformations_ and coding RGB JPEG
 - Decoder can decompress JPEG codestreams that can be generated by encoder. If scan
   contains restart flags, decoder can use parallelism for fast decoding.
--  _command-line_ tool with support for encoding/decoding **raw** images as well as **PNM/PAM** or **Y4M**
+-  _command-line_ tool with support for encoding/decoding **raw** images
+as well as **BMP**, **TGA**, **PNM/PAM** or **Y4M**
 
 Overview
 --------
@@ -448,6 +449,8 @@ License
 - See file [COPYING](COPYING).
 - This software contains source code provided by NVIDIA Corporation.
 - This software source code is based on SiGenGPU \[[3]\].
+- Thanks [notings/stb](https://github.com/nothings/stb) (BMP+TGA image
+support, public domain).
 
 References
 ----------