fix image links in readme

README.md

@@ -11,7 +11,7 @@ Super Jibby 2 uses the palette and colour data encoded in false-colour RGBA text
 ### Image-Encoded Palette (IEP) Shader
 
 <p align="center">
-    <img src="https://github.com/mstop4/super-jibby-2/blob/master/doc/iep%20example.png" width=50%>
+    <img src="https://github.com/mstop4/super-jibby-2/blob/main/doc/iep%20example.png" width=50%>
 </p>
 
 Palette indices are encoded in the red channel while colour indices within a palette are encoded in the green channel. This shader is useful for images that use multiple static palettes.
@@ -21,7 +21,7 @@ Palette indices are encoded in the red channel while colour indices within a pal
 ### Manually-Encoded Palette (MEP) Shader
 
 <p align="center">
-    <img src="https://github.com/mstop4/super-jibby-2/blob/master/doc/mep%20example.gif" width=50%>
+    <img src="https://github.com/mstop4/super-jibby-2/blob/main/doc/mep%20example.gif" width=50%>
 </p>
 
 Like with the IEP shader, colour indices within a palette are encoded in the green channel, but only a single palette index is passed to the shader via a uniform. This shader is useful for images that have a single, swappable palette.