Fix vgv-wingspan installation command on README

[3ettilina]

Description

This PR aims to fix the installation guidelines, as they weren't properly working when attempting to install the vgv-wingspan plugin within Claude Code session or in bash.

Proof

Error obtained with README instructions

With fix

Inside Claude Code session

Bash

claude plugin marketplace add VeryGoodOpenSource/very_good_claude_marketplace && claude plugin install vgv-wingspan                             
✔ Marketplace 'very-good-claude-code-marketplace' already on disk — declared in user settings
✔ Successfully installed plugin: vgv-wingspan@very-good-claude-code-marketplace (scope: user)

Type of Change

• New feature (feat)
• Bug fix (fix)
• Code refactor (refactor)
• Documentation (docs)
• CI change (ci)
• Chore (chore)