Instructions to build this project

How do I build this project on my local machine? Which version of Gradle should I use?

Gradle 6.7 fails with the following error:
```
$ gradle build

FAILURE: Build failed with an exception.

* Where:
Build file '~/devel/plugin-repository-rest-client/build.gradle' line: 2

* What went wrong:
Plugin [id: 'org.jetbrains.kotlin.jvm'] was not found in any of the following sources:

- Gradle Core Plugins (plugin is not in 'org.gradle' namespace)
- Plugin Repositories (plugin dependency must include a version number for this source)

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 448ms
```