feat: modify GH actions according to README

[quartztz]

Response to :

2. Set up Github Actions

This repo includes a workflow called build_pdf.yml that uses GitHub Actions to automatically generate a PDF of your PRD.

After cloning this repo, customize the workflow for your own team by editing the workflow as follows:

• Line 40: Set the right team number, by replacing 26 with your team's number here;
• Line 46: Same for the PDF artifact's name (replace 26 with your team's number) here.

in the provided README.md. This modifies 26 to 20