Added note of caution in minimum_spanning_tree(_parallel) (#199)

Author: sar99

pydatastructs/graphs/algorithms.py

@@ -265,6 +265,14 @@ def minimum_spanning_tree(graph, algorithm):
     ==========
 
     .. [1] https://en.wikipedia.org/wiki/Kruskal%27s_algorithm
+
+    Note
+    ====
+
+    The concept of minimum spanning tree is valid only for
+    connected and undirected graphs. So, this function
+    should be used only for such graphs. Using with other
+    types of graphs may lead to unwanted results.
     """
     import pydatastructs.graphs.algorithms as algorithms
     func = "_minimum_spanning_tree_" + algorithm + "_" + graph._impl
@@ -337,6 +345,14 @@ def minimum_spanning_tree_parallel(graph, algorithm, num_threads):
     ==========
 
     .. [1] https://en.wikipedia.org/wiki/Kruskal%27s_algorithm#Parallel_algorithm
+
+    Note
+    ====
+
+    The concept of minimum spanning tree is valid only for
+    connected and undirected graphs. So, this function
+    should be used only for such graphs. Using with other
+    types of graphs will lead to unwanted results.
     """
     import pydatastructs.graphs.algorithms as algorithms
     func = "_minimum_spanning_tree_parallel_" + algorithm + "_" + graph._impl