Recommend link to COmmunity Marketplace in README

[jonathanofsmith]

README says this was depreciated but I think should also include a link to the replacement (https://community.microstrategy.com/t5/Visualization-Library/bg-p/vizgallery)

[ffniu]

Thanks for your good suggestion. Actually, there are links to all replacement places, like Visualization Gallery, and Developer Zone, etc. Any other concern, let us know. Thanks.