Use https://github.com/Kotlin/dataframe/tree/example-projects-archives links more widely in example READMEs

We have a page with link for direct download of project directories: https://github.com/Kotlin/dataframe/tree/example-projects-archives

We don't have these links in root readme for examples: https://github.com/Kotlin/dataframe/tree/master/examples

Only in some of project specific READMEs https://github.com/Kotlin/dataframe/tree/master/examples/projects/kotlin-dataframe-plugin-gradle-example and https://github.com/Kotlin/dataframe/tree/master/examples/projects/kotlin-dataframe-plugin-maven-example

Start with the README for examples at https://github.com/Kotlin/dataframe/tree/master/examples and compare it with the project-specific READMEs that already contain archive links. Add the direct-download link where it is missing across the relevant example READMEs, then verify that users can find the project archive from each example entry.

Written by the indexing model from the issue text.