docs: add troubleshooting for slow performance

[hummusonrails]

Description

Add a troubleshooting section for slow performance in the LSP server advising users on steps to mediate it.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[sdankel]

This has already been done: https://fuellabs.github.io/sway/v0.52.0/book/lsp/troubleshooting.html

Ah sorry I didn't see that you were just adding to the page.