Fix add_surface_from_arrays description in classref

Fix add_surface_from_arrays description in ImporterMesh.xml and ArrayMesh.xml to correctly describe sub-array length requirements.

Also add missing comma in MeshInstance3D.xml, reword slightly.

doc/classes/ArrayMesh.xml

@@ -67,7 +67,7 @@
 			<description>
 				Creates a new surface.
 				Surfaces are created to be rendered using a [code]primitive[/code], which may be any of the types defined in [enum Mesh.PrimitiveType]. (As a note, when using indices, it is recommended to only use points, lines, or triangles.) [method Mesh.get_surface_count] will become the [code]surf_idx[/code] for this new surface.
-				The [code]arrays[/code] argument is an array of arrays. See [enum Mesh.ArrayType] for the values used in this array. For example, [code]arrays[0][/code] is the array of vertices. That first vertex sub-array is always required; the others are optional. Adding an index array puts this function into "index mode" where the vertex and other arrays become the sources of data and the index array defines the vertex order. All sub-arrays must have the same length as the vertex array or be empty, except for [constant Mesh.ARRAY_INDEX] if it is used.
+				The [code]arrays[/code] argument is an array of arrays. See [enum Mesh.ArrayType] for the values used in this array. For example, [code]arrays[0][/code] is the array of vertices. That first vertex sub-array is always required; the others are optional. Adding an index array puts this function into "index mode" where the vertex and other arrays become the sources of data and the index array defines the vertex order. All sub-arrays must have the same length as the vertex array (or be an exact multiple of the vertex array's length, when multiple elements of a sub-array correspond to a single vertex) or be empty, except for [constant Mesh.ARRAY_INDEX] if it is used.
 			</description>
 		</method>
 		<method name="clear_blend_shapes">

doc/classes/ImporterMesh.xml

@@ -30,7 +30,7 @@
 			<description>
 				Creates a new surface, analogous to [method ArrayMesh.add_surface_from_arrays].
 				Surfaces are created to be rendered using a [code]primitive[/code], which may be any of the types defined in [enum Mesh.PrimitiveType]. (As a note, when using indices, it is recommended to only use points, lines, or triangles.) [method Mesh.get_surface_count] will become the [code]surf_idx[/code] for this new surface.
-				The [code]arrays[/code] argument is an array of arrays. See [enum Mesh.ArrayType] for the values used in this array. For example, [code]arrays[0][/code] is the array of vertices. That first vertex sub-array is always required; the others are optional. Adding an index array puts this function into "index mode" where the vertex and other arrays become the sources of data and the index array defines the vertex order. All sub-arrays must have the same length as the vertex array or be empty, except for [constant Mesh.ARRAY_INDEX] if it is used.
+				The [code]arrays[/code] argument is an array of arrays. See [enum Mesh.ArrayType] for the values used in this array. For example, [code]arrays[0][/code] is the array of vertices. That first vertex sub-array is always required; the others are optional. Adding an index array puts this function into "index mode" where the vertex and other arrays become the sources of data and the index array defines the vertex order. All sub-arrays must have the same length as the vertex array (or be an exact multiple of the vertex array's length, when multiple elements of a sub-array correspond to a single vertex) or be empty, except for [constant Mesh.ARRAY_INDEX] if it is used.
 			</description>
 		</method>
 		<method name="clear">

doc/classes/MeshInstance3D.xml

@@ -4,7 +4,7 @@
 		Node that instances meshes into a scenario.
 	</brief_description>
 	<description>
-		MeshInstance3D is a node that takes a [Mesh] resource and adds it to the current scenario by creating an instance of it. This is the class most often used render 3D geometry and can be used to instance a single [Mesh] in many places. This allows reuse of geometry which can save on resources. When a [Mesh] has to be instantiated more than thousands of times at close proximity, consider using a [MultiMesh] in a [MultiMeshInstance3D] instead.
+		MeshInstance3D is a node that takes a [Mesh] resource and adds it to the current scenario by creating an instance of it. This is the class most often used render 3D geometry and can be used to instance a single [Mesh] in many places. This allows reusing geometry, which can save on resources. When a [Mesh] has to be instantiated more than thousands of times at close proximity, consider using a [MultiMesh] in a [MultiMeshInstance3D] instead.
 	</description>
 	<tutorials>
 		<link title="3D Material Testers Demo">https://godotengine.org/asset-library/asset/123</link>