docs: add guide for resolving contract addresses

[piyushbag]

Problem

No open maintainer issues in justlend-docs. Integrators repeatedly hard-code jToken addresses instead of using the canonical registry.

Approach

Add Resolving Contract Addresses developer guide covering contracts.json fields, jToken lookup by underlying symbol, REST API fallback, and Moolah V2 identifiers. Fix a punctuation typo in Contracts Overview.

Test plan

• mkdocs nav entry added
• mkdocs build --strict in CI

FALLBACK: no maintainer-authored issues; docs-only contribution in the JustLend org.

[BlackChar92]

Thanks for the contribution and for identifying the need for a contract-address resolution guide.
We have now merged #94, which addresses the same documentation gap while aligning the examples with the current nested contracts.json schema, API response fields, and JustLend V2 boundaries.
Since this PR has been superseded by #94 and now conflicts with main, we’ll close it. We appreciate the proposal—it helped surface an important documentation gap.