Limbo.Umbraco.Rte is small package that brings extended functionality to Umbraco's build-in rich text editor (TinyMCE). The package does so by adding a new Limbo RTE property editor, which enables developers to select a number of processors, that may modify the HTML - eg. to ensure that external links always open in a new window/tab.
This is the recommend approach, as you install the NuGet Package in your Visual Studio project, and NuGet takes care of the rest.
Umbraco 10
Latest release for Umbraco 10 is v2.0.0:
Install-Package Limbo.Umbraco.Rte-Version 2.0.0
Umbraco 9
Latest release for Umbraco 9 is v1.0.0:
Install-Package Limbo.Umbraco.Rte-Version 1.0.0