Add Git post-checkout hook documentation for automatic Jira status updates

[Copilot]

This PR adds comprehensive documentation for a Git post-checkout hook that automatically updates Jira issue status when developers switch branches.

What's Added

A new Git Hook Integration section in the README that documents a bash script for automatically syncing Git branch changes with Jira. When a developer checks out a branch with a Jira issue key in the name (e.g., feature/PROJ-123-add-feature), the hook automatically updates that issue's status to "In Progress".

Key Features Documented

• Automatic detection: Extracts Jira issue keys from branch names using the pattern [_A-Z0-9]+-[0-9]+
• Self-installing: Downloads the jira CLI automatically if not present in ~/bin/jira
• Platform-aware: Detects the correct binary for the user's OS and architecture
• Zero-friction workflow: Developers just check out branches normally, and Jira stays in sync

Documentation Includes

1. Clear explanation of what the hook does and why it's useful
2. Step-by-step setup instructions
3. The complete bash script ready to copy-paste
4. Examples of supported branch naming conventions
5. Notes about customizing for different Jira instances

This enhancement helps teams maintain better synchronization between their Git workflow and Jira project tracking without requiring manual updates.

Original prompt

Add this to the README, explain what it is

#!/bin/bash
set -euo pipefail

old_branch=$(git name-rev --name-only "$1")
new_branch=$(git branch --show-current)

if [ "$old_branch" = "$new_branch" ]; then
exit 0
fi

grep the branch name for a jira ticket pattern (e.g. ABC-123)

jira_issue_key=$(echo $new_branch | grep -oE '[_A-Z0-9]+-[0-9]+')

if [ ! -n "$jira_issue_key" ]; then
exit
fi

if [ ! -e ~/bin/jira ]; then
platform=$(uname -s | tr '[:upper:]' '[:lower:]')
arch=$(uname -m | sed 's/x86_64/amd64/' | sed 's/aarch64/arm64/')
curl -fsL -o ~/bin/jira https://github.com/kitproj/jira-cli/releases/download/v0.0.6/jira_v0.0.6_${platform}_${arch}
mkdir -p ~/bin
chmod +x ~/bin/jira
fi

~/bin/jira -h jira.intuit.com update-issue-status $jira_issue_key "In Progress"

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