Update README

Author: mtfishman

README.md

@@ -82,8 +82,7 @@ function main()
   @test b[Block(1, 2)] == a₁₂
 
   # Matrix multiplication
-  # TODO: Fix this, broken.
-  @test_broken b * b ≈ Array(b) * Array(b)
+  @test b * b ≈ Array(b) * Array(b)
 
   permuted_b = permutedims(b, (2, 1))
   @test permuted_b isa BlockSparseArray