Add auto to the list of sizes (#23786)

I feel like `auto` is missing from the values here and that it should be there. Although it is mentioned below, only a single use case, whereas in other sections it appears with the option to set the left margin of an element to auto, for example.

diff --git a/docs/4.0/utilities/spacing.md b/docs/4.0/utilities/spacing.md
index d6d2d7b5405295060af6ae7e99eab3f5490a3f88..035a337afec24782d90970fc23d631cc4fd361b0 100644 (file)
--- a/docs/4.0/utilities/spacing.md
+++ b/docs/4.0/utilities/spacing.md
@@ -39,6 +39,7 @@ Where *size* is one of:
 * `3` - (by default) for classes that set the `margin` or `padding` to `$spacer`
 * `4` - (by default) for classes that set the `margin` or `padding` to `$spacer * 1.5`
 * `5` - (by default) for classes that set the `margin` or `padding` to `$spacer * 3`
+* `auto` - for classes that set the `margin` to auto
 
 (You can add more sizes by adding entries to the `$spacers` Sass map variable.)