fix broken images on opensource.axo.dev

make all image links relative so that they work when deployed on
...axo.dev/oranda/

docs/src/configuration/theme/previews.md

@@ -6,25 +6,25 @@ These previews are generated by running oranda on itself.
 
 ## Dark (default)
 
-![dark theme preview](/images/themes/dark.jpg)
+![dark theme preview](../../images/themes/dark.jpg)
 
 ## Light
 
-![light theme preview](/images/themes/light.jpg)
+![light theme preview](../../images/themes/light.jpg)
 
 ## Axo Dark
 
-![axo dark theme preview](/images/themes/axodark.jpg)
+![axo dark theme preview](../../images/themes/axodark.jpg)
 
 ## Axo Light
 
 
-![axo light theme preview](/images/themes/axolight.jpg)
+![axo light theme preview](../../images/themes/axolight.jpg)
 
 ## Hacker
 
-![hacker theme preview](/images/themes/hacker.jpg)
+![hacker theme preview](../../images/themes/hacker.jpg)
 
 ## Cupcake
 
-![cupcake preview](/images/themes/cupcake.jpg)
+![cupcake preview](../images/themes/cupcake.jpg)