Doc Updates

[yanmastin-astro]

Description

The purpose of this PR is to improve the docs in the Astro terraform registry listing.

The files in the docs folder are autogenerated from default templates by the tfplugindocs tool during the build. You can overwrite the default templates using .tmpl files in the templates folder which is added in this PR. You can also add .md files into the templates/guides folder to add markdown formatted user guides.

This PR:

Improves the Astro Terraform Provider listing doc homepage by adding a index.md.tmpl file that has high level descriptions, authentication information, in addition to the existing autogenerated Example Usage and Schema sections.
Adds a get-started.md guide that walks through a simple example use case of Astro Terraform Provider.
Adds a import-script.md guide that shows how to use the import script to automate the migration of existing resources into Terraform.

🧪 Functional Testing

Manual review

[ichung08]

thanks for taking the time to make the adjustments we discussed last week! this looks much better now

a few small comments but overall looks good to me

[lzdanski]

@yanmastin-astro This is fantastic work! My feedback is almost completely style guide conventions that are more or less variations on:

• reduce future tense and 'to be' verb constructions
• Position the voice to be "Astronomer recommends" vs "we recommend"

🎉 fantastic. Almost there!