[Apps][Examples] Update examples list

Summary: As per feedback in D14360, replacing the smart contract examples with alternate examples.

Test Plan: plonk README into https://jbt.github.io/markdown-editor/

Reviewers: bytesofman, #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14365