Add upgrade documentation for 1.5 to 2.0
Add upgrade documentation for 1.5 to 2.0

huminzhi/SalesforceMobileSDK-Android,kchitalia/SalesforceMobileSDK-Android,seethaa/force_analytics_example,solomonronald/SalesforceMobileSDK-Android,kchitalia/SalesforceMobileSDK-Android,seethaa/force_analytics_example,solomonronald/SalesforceMobileSDK-Android,kchitalia/SalesforceMobileSDK-Android,seethaa/force_analytics_example,huminzhi/SalesforceMobileSDK-Android,solomonronald/SalesforceMobileSDK-Android,huminzhi/SalesforceMobileSDK-Android