spec: document conversion from slice to array

Document that a slice can be converted to either an array or a pointer
to an array of a matching underlying array type. This was documented in
the "Conversions from slice to array or array pointer" subsection, but
not in the list of conversion rules.

Updates #46505.

Change-Id: I16a89a63ef23c33580129952415e977a8f334009
Reviewed-on: https://go-review.googlesource.com/c/go/+/452936
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>
Run-TryBot: Tim King <[email protected]>

doc/go_spec.html

@@ -5348,7 +5348,7 @@ <h3 id="Conversions">Conversions</h3>
 	<code>x</code> is a string and <code>T</code> is a slice of bytes or runes.
 	</li>
 	<li>
-	<code>x</code> is a slice, <code>T</code> is a pointer to an array,
+	<code>x</code> is a slice, <code>T</code> is an array or a pointer to an array,
 	and the slice and array types have <a href="#Type_identity">identical</a> element types.
 	</li>
 </ul>