Merge pull request carpentries-incubator/issues/31 from aflaxman/patch-1

Edit introduction paragraph for gentler intro

episodes/01-singularity-gettingstarted.md

@@ -44,7 +44,11 @@ Working with Singularity containers:
 
 ## What is Singularity?
 
-[Singularity](https://sylabs.io/singularity/) is another container platform. In some ways it appears similar to Docker from a user perspective, but in others, particularly in the system's architecture, it is fundamentally different. These differences mean that Singularity is particularly well-suited to running on distributed, High Performance Computing (HPC) infrastructure, as well as a Linux laptop or desktop! 
+[Singularity](https://sylabs.io/singularity/) is a container platform that allows software engineers and researchers to easily share their work with others by packaging and deploying their software applications in a portable and reproducible manner. When you download a Singularity container image, you essentially receive a virtual computer disk that contains all of the necessary software, libraries and configuration to run one or more applications or undertake a particular task, e.g. to support a specific research project. This saves you the time and effort of installing and configuring software on your own system or setting up a new computer from scratch, as you can simply run a Singularity container from the image and have a virtual environment that is identical to the one used by the person who created the image. Container platforms like Singularity provide a convenient and consistent way to access and run software and tools. Singularity is increasingly widely used in the research community for supporting research projects as it allows users to isolate their software environments from the host operating system and can simplify tasks such as running multiple experiments simultaneously.
+
+You may be familiar with Docker, another container platform that is now used widely. If you are, you will see that in some ways, Singularity is similar to Docker. However, in others, particularly in the system's architecture, it is fundamentally different. These differences mean that Singularity is particularly well-suited to running on distributed, High Performance Computing (HPC) infrastructure, as well as a Linux laptop or desktop! 
+
+_Later in this material, when we come to look at building Singularity images ourselves, we will make use of Docker to provide an environment in which we can run Singularity with administrative privileges. In this context, some basic knowledge of Docker is strongly recommended. If you are covering this module independently, or as part of a course that hasn't covered Docker, you can find an introduction to Docker in the "[Reproducible Computational Environments Using Containers: Introduction to Docker](https://carpentries-incubator.github.io/docker-introduction/index.html)" lesson._
 
 System administrators will not, generally, install Docker on shared computing platforms such as lab desktops, research clusters or HPC platforms because the design of Docker presents potential security issues for shared platforms with multiple users. Singularity, on the other hand, can be run by end-users entirely within "user space", that is, no special administrative privileges need to be assigned to a user in order for them to run and interact with containers on a platform where Singularity has been installed.