Consistent terminology throughout documentation

[dc2007git]

Having a read through documentation, it looks like there are a few different names we're throwing around for the component and client, such as library, package. It's a small thing, but when working through new documentation I think consistent language is important for user clarity.

This issue doesn't need to stay open forever, if there is somewhere better we can put it then let's do that. Just a gentle reminder!

@mbarton @eatyourpeas @pacharanero @anchit-chandran

[pacharanero]

[moved from rcpch/digital-growth-charts-documentation repo]