Update the playbook with info about blog post creation

[LouWoodley]

This issue tracks the updating of the playbook with information and instructions about how to draft new blog posts for the CP blog.

It is done when the playbook is updated and the team is emailed with an update (as per the website launch)

[jnywong]

I've created a new issue template for adding blog posts to the website

https://github.com/czi-catalystproject/czi-catalystproject.github.io/issues/new/choose

Relevant updates are also in https://github.com/czi-catalystproject/czi-catalystproject.github.io/issues/42#issuecomment-2075067983

[Tajuddeen1]

I have updated the playbook