Add planar lemmas

[Bezaliel Silva]

Let G = (V, E) be a connected planar graph. Let F be the set of faces of a planar drawing of G. Then |V | − |E| + |F| = 2.
If G = (V, E) is a connected planar graph and |V | > 2, then |E| ≤ 3|V | − 6.