docs: revise readme

[inventarSarah]

A summary of the changes:

• fix typos and the likes
• add "alerts" to highlight information and make text more interesting
• add list of integrations at the top
• put sponsor/donor-related information into one section
• add a new section that describes the basics of writing tests
  • moved some content from the "best practices" and "integration" sections in there but also added new content
• streamline integrations section to focus on their benefits and what sets them apart (repeating information (eg what types of locations you can provide) have been moved to the "get started writing tests" section
• restructure Best practice section
  • moved "basic" information to the new section
  • created a subsection that talks about location-specific tips
  • moved everything that is not a best practice into a new section, "things to keep in mind"
  • I also added emojis here - it helps make the text look more interesting and because we want to have more interesting headers here anyway, I thought it would be a good fit
• added a support and feedback section

[jimaek]

I stopped the review at the last comment, will continue after the updates. Also we're about to ship a new feature https://github.com/jsdelivr/globalping/pull/453 Lets document it here as well.

I think it should be in the tips and tricks section and maybe a mention in the CLI section. The idea is that the magic field can accept not just locations but also previous measurement IDs to select the exact same probes. This is useful for running comparisons of endpoints from the same probes for better data. Or to run continuous tests from the same probes

[inventarSarah]

RE. new feature #453

Updated the content with info about new feature -> still WIP as I need to add examples (added placeholders)

• added info to the "Location" section within "basics of writing tests"
• added a new section in under "best practices"
• added info to the "no UUIDs" section

[inventarSarah]

RE. new feature #453

Updated the content with info about new feature -> still WIP as I need to add examples (added placeholders)

• added info to the "Location" section within "basics of writing tests"
• added a new section in under "best practices"
• added info to the "no UUIDs" section

I reworked the section with the available information and added examples. Once we're happy with the readme, I can move the content for the new feature in a separate PR so you can release it when the feature's available (let me know if we should do this)

[jimaek]

Thank you