Update README.md

Author: scheinerman

README.md

@@ -86,6 +86,7 @@ julia> T = Tableau(A, b, c, false)
 │   Cons 2 │ 0 │   1 │   1 │  -1 │   5 │   1 │   7 │
 └──────────┴───┴─────┴─────┴─────┴─────┴─────┴─────┘
 ```
+The fourth argument `false` means that the constraints are already equalities and slack variables should not be appended. 
 
 ## Operations