Adding cpdag extension algorithms

Signed-off-by: Adam Li <[email protected]>

doc/api.rst

@@ -67,7 +67,7 @@ causal graph operations.
 :mod:`pywhy_graphs.algorithms.cpdag`: Algorithms for dealing with CPDAGs
 ========================================================================
 With Markov equivalence classes of DAGs in a Markovian SCM setting, we obtain
-a potentiallly directed acyclic graph (PDAG), which may be completed (CPDAG).
+a potentially directed acyclic graph (PDAG), which may be completed (CPDAG).
 We may want to generate a consistent DAG extension (i.e. Markov equivalent) of a CPDAG
 then we may use some of the algorithms described here. Or perhaps one may want to 
 convert a DAG to its corresponding CPDAG.