Add PFM format support to README.md

README.md

@@ -7,6 +7,7 @@ A high dynamic range (HDR) image comparison tool for graphics people. __tev__ al
 
 While the predominantly supported file format is OpenEXR certain other types of images can also be loaded. The following file formats are currently supported:
 - __EXR__ (via [OpenEXR](https://github.com/wjakob/openexr))
+- __PFM__
 - __HDR__, BMP, GIF, JPEG, PIC, PNG, PNM, PSD, TGA (via [stb_image](https://github.com/wjakob/nanovg/blob/master/src/stb_image.h))
     - stb_image only supports [subsets](https://github.com/wjakob/nanovg/blob/master/src/stb_image.h#L23) of each of the aforementioned file formats.
     - Low-dynamic-range (LDR) images are "promoted" to HDR through the reverse sRGB transformation.