Add Palm in themes

Author: dks333

settings/global.mdx

@@ -25,7 +25,7 @@ Every documentation site requires a `docs.json` file that contains the core conf
 
 ### Customization
 
-<ResponseField name="theme" type='"mint" | "maple"' required>
+<ResponseField name="theme" type='"mint" | "maple" | "palm"' required>
   The layout theme of the project
 </ResponseField>