docs: add pitch deck link

Author: MarcusDavidG

README.md

@@ -21,6 +21,7 @@ Soroban smart contract powering the Sharpy split payment protocol on Stellar. Ha
 
 - [Testnet Explorer](https://stellar.expert/explorer/testnet/contract/CAYTIFPD6RFWVHMK5SPPUUIWWAAANHKOJB6GOAJS5SR5MBKZMEY2UODZ)
 - [Frontend dApp](https://sharpy-sigma.vercel.app)
+- [Pitch Deck](https://gamma.app/docs/Split-Payments-on-Stellar-s0et8z1agtva59n)
 
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