add coalesced argument to README

Author: rusty1s

README.md

@@ -202,6 +202,7 @@ Both input sparse matrices need to be **coalesced**.
 * **m** *(int)* - The first dimension of first corresponding dense matrix.
 * **k** *(int)* - The second dimension of first corresponding dense matrix and first dimension of second corresponding dense matrix.
 * **n** *(int)* - The second dimension of second corresponding dense matrix.
+* **coalesced** *(bool, optional)*: If set to `True`, will coalesce both input sparse matrices (default: `False`).
 
 ### Returns