refer from

gitbook 的基本用法非常简单，基本上就只有两步：

1. 使用 gitbook init 初始化书籍目录
2. 使用 gitbook serve 编译书籍
3. npm install -g gitbook-summary ,use 'book sm' to generate a SUMMARY.md

refer

1. cd $note gitbook epub ./ note.epub gitbook mobi ./ note.mobi gitbook pdf note.pdf

modify gitbook-summary/lib/summary/index.js

function work(filesObj) {
    _.forEach(filesObj, function(n, key) {
        if (!_.includes(ignores, key)) {
            if (_.isObject(n)) {

                // The file is `readme.md`
                if (_.isString(n['readme']) || _.isString(n['Readme']) || _.isString(n['README'])) {
                    var readmeDir = n['readme'] || n['Readme'] || n['README'];
                    desc += _.repeat(' ', step) + formatCatalog(key, '-') + readmeDir;
                } else {
                    desc += _.repeat(' ', step) + "- " + prettyCatalogName(key) + "\n";
                }

                // It means folderName == subFileName, for example: */assets/assets.md or */Assets/assets.md
                if (_.isString(n[key]) || _.isString(n[key.toLowerCase()])) {
                    var file = n[key] || n[key.toLowerCase()];
                    step += 2;
                    desc += _.repeat(' ', step) + formatCatalog(key, '*') + file;
                    step -= 2;

                    // Mark it to skip
                    skip = key;
                }
                // Start a loop
                step += 2;
                work(n);
                step -= 2;
            } else {
                // Skip if `skip` exists or key == `readme`
                if (isSkiped(key, skip)) {
                    return;
                }

                desc += _.repeat(' ', step) + formatCatalog(key) + n;
            }
        }
    });
}