Generate PR Description

You are tasked with generating a comprehensive pull request description following the repository's standard template.

Steps to follow:

1. Read the PR description template:

   • First, check if thoughts/shared/pr_description.md exists
   • If it doesn't exist, inform the user they need to create a PR description template at thoughts/shared/pr_description.md
   • Read the template carefully to understand all sections and requirements

2. Identify the PR to describe:

   • Check if the current branch has an associated PR: gh pr view --json url,number,title,state 2>/dev/null
   • If no PR exists for the current branch, or if on main/master, list open PRs: gh pr list --limit 10 --json number,title,headRefName,author
   • Ask the user which PR they want to describe