Fix Typos in Staking Script Documentation

[Dimitrolito]

This pull request corrects two grammatical issues in the staking-script.md file:

1. Changed "the an" to "an" for proper article usage in the Finality Provider section.
2. Updated "system wide" to "system-wide" for correct hyphenation when used as an adjective.

Motivation

Ensuring clarity and grammatical correctness in the documentation enhances its readability and professionalism.

Changes

• File: docs/staking-script.md
  • Two additions and two deletions to fix grammar and hyphenation issues.

Testing

No functional changes—only documentation updates.