Update README
Update README

Add Spring Solver info and make other small changes.

DZNS/AnimationEngine,intuit/AnimationEngine,quyixia/AnimationEngine,DZNS/AnimationEngine,intuit/AnimationEngine,msdgwzhy6/AnimationEngine,msdgwzhy6/AnimationEngine,DZNS/AnimationEngine,msdgwzhy6/AnimationEngine,quyixia/AnimationEngine,quyixia/AnimationEngine