docs: correct P2ID note count and loop range in mint tutorial

[memosr]

The paragraph introducing the multi-note output snippet describes five notes
over 0..=4, but the code creates four notes over 1..=4.

Three sources in the repo already agree on four:

• rust-client/src/bin/create_mint_consume_send.rs prints
  Submitted a transaction with 4 P2ID notes
• the code fence further down this same file uses 1..=4
• line 140 of this same file already says "the first four P2ID transfers are
  handled in a single transaction, and the fifth transfer is a standard P2ID
  transfer"

So the paragraph contradicted both the code below it and the prose six lines
above it. This aligns the wording with all three.

Text-only change, no code touched. cargo test --doc in docs/ passes
(17 passed, 0 failed). Ran prettier --write per CONTRIBUTING.md; the line
was already conformant.