Update README: Re-organize headers, make <details> open, and emphasize cookie filename pattern

[Hansimov]

Here are the changes to the README.md, with details and reasons.

1. Re-organize headers

   • Put header Authentication and Collect cookies besides Requirements
     • Reason: Because these two steps are also required before running the script, so it would
   • Modify some names of headers
     • Reason: To make the headers more clear and easy to understand

2. Modify <details> tags

   • Make all <details> tags to <details open>
     • Reason: The main goal of doc is to make the users and developers to quickly setup, run and search the project. It is quite inconvenient for users to click once each time to expand the collapsed contents.
   • Also remove some unnecessary <details> tags. Only preserve the first-level ones.
     • Reason: Nested structure always makes people confused and lost in steps.

3. Emphasize the cookies regex pattern bing_cookies_*.json

   • Use NOTE and bold text draw users' attention
     • Reason: This step usually challenges the first-time users.