docs: add class 1 stablecoin issuance walkthrough

[Edugera]

Summary

This PR adds a walkthrough for Class 1, describing it as the minimum issuance lifecycle of a fictional Stellar-based stablecoin.

It explains:

• issuer, distributor, and holder roles;
• asset identity as CODE:ISSUER;
• trustline-based consent;
• supply distribution;
• the expected op_no_trust failure;
• the difference between an educational testnet simulation and a production-grade stablecoin.

Motivation

The goal is to make the Class 1 learning path clearer for developers who are new to Stellar classic assets.

Class 1 is important because it shows that a token is not only an asset code, but a CODE:ISSUER pair, and that receiving a non-native asset requires explicit holder consent through a trustline.

[Edugera]

Thanks for the repository and the learning path.

I added this walkthrough as a first contribution to make Class 1 easier to follow for developers who are new to Stellar classic assets.

My understanding is that Class 1 demonstrates the minimum technical issuance lifecycle of a fictional stablecoin on testnet: issuer, asset identity, trustline consent, supply distribution, and the expected op_no_trust failure when consent is missing.

Happy to adjust the wording or structure if you prefer a different documentation style.