Writing of Voltage-current Relationship

Wrote the very first part of result section. This commit covers
descriptions on the relationship between voltage and current. Also, I
attached the plots describing the relationship between wire length and
current.
(#3) Writing cross-sectional area part in result

Wrote cross-sectional area part in result. This includes just text.
Merge pull request #6 from lightphh/cross-section-result

Cross section result