Generate Bevy migration guide stub

generate-guide-stub.sh

#!/usr/bin/env zsh

# TODO not sure why this doesn't work in bash

if ! hash markdown-extract &> /dev/null
then
    echo "markdown-extract required"
    echo "cargo install markdown-extract"
    exit 1
fi

if ! hash gh &> /dev/null
then
    echo "github cli required"
    echo "https://github.com/cli/cli"
    exit 1
fi

echo > out.md
for PR in $(git log 'v0.8.0'..HEAD --oneline | grep -o '(#\d\+)' | grep -o '\d\+')
do
    TEXT=$(gh pr view $PR)
    TITLE=$(echo $TEXT | head -n 1 | sed 's/^.*Bors\] - //')
    OUT=$(echo $TEXT | markdown-extract -n "Migration Guide" /dev/stdin)
    if [ $? -eq 0 ]; then
        echo "\n### [$TITLE](https://github.com/bevyengine/bevy/pull/$PR)\n" >> out.md
        echo $OUT >> out.md
    fi
done