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.
Latest release for Umbraco 10 is v2.0.0:
Install-Package Limbo.Umbraco.Rte-Version 2.0.0
Latest release for Umbraco 9 is v1.0.0:
Install-Package Limbo.Umbraco.Rte-Version 1.0.0