docs: update --set

Signed-off-by: aevesdocker <[email protected]>

Author: aevesdocker

docs/reference/buildx_bake.md

@@ -410,6 +410,12 @@ $ docker buildx bake --set foo*.no-cache                # bypass caching only fo
 $ docker buildx bake --set target.platform+=linux/arm64 # appends 'linux/arm64' to the platform list
 ```
 
+`--set` is a repeatable flag. For array fields such as `tags`, repeat `--set` to provide multiple values or use the `+=` operator to append without replacing.
+
+Array literal syntax like `--set target.tags=[a,b]` is not supported.
+
+The `platform` field is a special case. it also accepts a comma-separated list.
+
 You can override the following fields:
 
 * `annotations`
@@ -451,3 +457,7 @@ You can append using `+=` operator for the following fields:
 
 > [!NOTE]
 > ¹ These fields already append by default.
+
+#### Examples
+
+