Convert these README files to markdown

border/gameboy-player/README.md

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+# Game Boy Player border shader
+
 These shader presets will allow you to apply a 608x448 Game Boy Player border around a 240x160 input image from a Game Boy Advance core, with the input being scaled 2x to fit the border.
 
 Please note that RetroArch's integer scaling function will not automatically set a correct integer scale for the output image, as it will only take the Game Boy Advance core's reported resolution of 240x160 into account, and not the output image's 608x448 resolution.

border/sgb/README.md

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+# Super Game Boy border shader
+
 These shader presets will allow you to apply a 256x224 Super Game Boy border around a 160x144 input image from a Game Boy core.
 
 Please note that RetroArch's integer scaling function will not automatically set a correct integer scale for the output image, as it will only take the Game Boy core's reported resolution of 160x144 into account, and not the output image's 256x224 resolution.

border/sgba/README.md

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+# Super Game Boy Advance border shader
+
 These shader presets will allow you to apply a 320x240 Super Game Boy Advance border around a 240x160 input image from a Game Boy Advance core.
 
 Please note that RetroArch's integer scaling function will not automatically set a correct integer scale for the output image, as it will only take the Game Boy Advance core's reported resolution of 240x160 into account, and not the output image's 320x240 resolution.