add citation information to readme?

[JieyuZ2]

add citation information to readme?

we can have two subsections there, one for the library: AutoGen & EcoOptiGen; and one for applications: MathChat (maybe this is also part of the library?)

[priyansh4320]

made changes to readme.md review and merge @JieyuZ2

[priyansh4320]

made changes to readme.md review and merge @JieyuZ2

[priyansh4320]

I have referred the docs for cite info and made changes accordingly. please review and merge @JieyuZ2

1. created a section contain cite to AutoGen and EcoOptGen
2. 2nd section cites to MathChat