[mlir] [linalg] Update documentation for fuse_into_containing_op

[harsh]

Summary

This patch updates the docs for fuse_into_containing_op. It
updates the returned values to include the new_containing_op
and adds a brief description of the new_containing_op.

updates the docs with new changes in the
op regarding the return of the new_containing_op as well
as a brief description o

mlir/include/mlir/Dialect/Linalg/TransformOps/LinalgTransformOps.td

def FuseIntoContainingOp :
     Op<Transform_Dialect, "structured.fuse_into_containing_op",
       [DeclareOpInterfaceMethods<TransformOpInterface,
           ["allowsRepeatedHandleOperands"]>,
        DeclareOpInterfaceMethods<MemoryEffectsOpInterface>]> {
   let summary = "Fuse a producer into a containing operation.";
 
   let description = [{
     Fuses the `producer_op` into the `containing_op`.
-    Returns a handle to the fused ops.
+    Returns a handle to the fused ops and the `new_containing_op`.
 
     The producer is typically a slice of a tileable op (i.e., implements
     TilingInterface). In that case, this transform computes the accessed
-    producer slice inside of the containing op ("tile and fuse"). Otherwise,
+    producer slice inside of the containing op ("tile and fuse") and if required,
+    creates a new containing op with outputs from the fused producer. Otherwise,
     the entire producer is cloned inside the containing op ("clone and fuse").
 
     The containing op handle must be associated with exactly one payload op. The
     producer op handle may be associated with multiple payload ops. This
     transform fuses producers one-by-one, always picking an unspecified producer
     that has at least one use inside the containing op among the
     producers. A producer can be listed multiple times in the handle.