fix: normals example uses backslash as path separator

[andrewwhitecdw]

This PR corrects the documentation in README.md: normals example uses backslash as path separator.

Changes

• README.md: normals example uses backslash as path separator.

Details

Before:

        normals/
            robot.front_camera.left.normals_image\
                00000000.npy
                00000001.npy
                ...

After:

        normals/
            robot.front_camera.left.normals_image/
                00000000.npy
                00000001.npy
                ...