Remove Hidden file in Keeper custom_luts directory.

Add documentation files about custom LUTs and custom patterns in the right
directories.

ColorTribe/ColorKeeper/colorkeeper_install_setup/custom_luts/README.md

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+## custom_luts directory ##
+___  
+
+Add here 2D LUTs you want to use as preview in ColorKeeper Toy tab.
+/!\ LUTs with values under 0 and above 1 are not handled.
+
+LUTs format : 
+
+0	0	0	0
+1	0	0	0
+2	0	0	0
+3	1	1	1
+4	2	2	2
+5	3	3	3
+6	3	3	3
+7	4	4	4
+8	5	5	5
+(...)
+255 	1023	1023	1023

ColorTribe/ColorKeeper/colorkeeper_install_setup/custom_patterns/README.md

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+## custom_patterns directory ##
+___  
+
+Add here images (jpg, png, tif) you want to use as references, they'll appear in ColorKeeper Calib tab.