This is a guided web course on creating an R script tool. It walks through the process of creating one on both the ArcGIS and R side. This is a good resources for first time script tool creation.
For users more comfortable with R scripting, the package vignette is a good resource because it provides a detailed description of each function in the arcgisbinding R package and can just be used as a resource versus a full tutorial like some of the above options. It also includes a template for creating script tools.
These sample script tools can be used as working examples to create new script tools off of.