fix: correct parameter count in token-swap README

[NikkiAung]

Summary

Fixes #494 — the walkthrough for swap_exact_tokens_for_tokens said it "takes five parameters" but only ever listed and described four: ctx, swap_a, input_amount, min_output_amount. The actual function signature (tokens/token-swap/anchor/programs/token-swap/src/instructions/swap_exact_tokens_for_tokens.rs) confirms it's 4 params, not 5.

Test plan

• Confirmed against the function signature that it has 4 parameters
• Docs-only change, no code affected

[greptile-apps]

Greptile Summary

Corrects the token-swap walkthrough to state that swap_exact_tokens_for_tokens takes four parameters, matching the four parameters documented immediately below.

Confidence Score: 5/5

The PR appears safe to merge because the documentation correction is internally consistent and introduces no runtime changes.

The revised count matches the four parameters enumerated in the walkthrough, and the change affects only explanatory documentation.

Important Files Changed

Filename	Overview
tokens/token-swap/README.md	Corrects an inaccurate parameter count from five to four without changing code or behavior.

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