Update config.mk comments a bit

# Package name and version

package = feh

version = 1.4.1

# Customize below:

# Prefix for all installed files

prefix = /usr/local

xinerama = -DHAVE_LIBXINERAMA

xinerama_ld = -lXinerama

# Put extra header directories here

# Put extra header (-I/some/directory) directories here

extra_headers =

# Put extra include (-Lfoo) directories here

# Put extra include (-L/some/directory) directories here

extra_libs =

debug = -DDEBUG

# Enable this for debug mode

# Uncomment this for debug mode

# (Use feh -+ <level> to see debug output)

#CFLAGS += $(debug)

dmalloc = -DWITH_DMALLOC

# Enable this to use dmalloc

# Uncomment this to use dmalloc

#CFLAGS += $(dmalloc)