Adds a note on .raw file extension to usage_examples.md

Adds a note on `.raw` file extension.

Author: aous72

docs/usage_examples.md

@@ -16,4 +16,5 @@ Here are some usage examples:
 * On Linux and MacOS, but NOT Windows, { and } need to be escaped; i.e, we need to write \\\{ and \\\}.  So, -block\_size {64,64} must be written as -block\_size \\\{64,64\\\}.
 * When the source is a .yuv file, use -downsamp {1,1} for 4:4:4 sources. For 4:2:2 downsampling, specify -downsamp {1,1},{2,1}, and for 4:2:0 subsampling specify -downsamp {1,1},{2,2}. The source must have already been downsampled (i.e., OpenJPH does not downsample the source before compression, but can compress downsampled sources).
 * In Kakadu, pairs of data in command line arguments represent columns,rows. Here, a pair represents x,y information.
+* It came to my realization (See https://github.com/aous72/OpenJPH/issues/187) that there is an issue with files with `.raw` extension.  Kakadu and OpenJPEG use `.raw` for big-endian data and `.rawl` for little-endian data -- This is only meaningful for data samples that are more than 1 byte.  OpenJPH uses `.raw` for little-endian and there is no support for big-endian.  I need to transition to the convention adopted by Kakadu and OpenJPEG; the plan to is to support `.rawl` first, and warning that `.raw` is currently little-endian, but the plan is to move to big-endian.  Then, at a future point, the warning for `.raw` becomes that it is for big-endian. Then after a while this warning can be removed.