Add About.jl to the Interactivity section (#140)

`about` is the go-to tool to get information about everything
and should therefore be mentioned directly after
`InteractiveUtils.jl` (and possibly even before).

Author: PatrickHaecker

writing/index.md

@@ -529,6 +529,7 @@ versioninfo()
 
 The following packages can give you even more interactive power:
 
+* [About.jl](https://github.com/tecosaur/About.jl) to look for detailed information about a function, type, value, or something else entirely.
 * [InteractiveCodeSearch.jl](https://github.com/tkf/InteractiveCodeSearch.jl) to look for a precise implementation of a function.
 * [InteractiveErrors.jl](https://github.com/MichaelHatherly/InteractiveErrors.jl) to navigate through stacktraces.
 * [CodeTracking.jl](https://github.com/timholy/CodeTracking.jl) to extend InteractiveUtils.jl