add nautygraphs/Igraphs to docs/Project.toml; add list of extended functions to docs

Author: mxhbl

docs/Project.toml

@@ -1,6 +1,8 @@
 [deps]
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
 Graphs = "86223c79-3864-5bf0-83f7-82e725a168b6"
+IGraphs = "647e90d3-2106-487c-adb4-c91fc07b96ea"
+NautyGraphs = "7509a0a4-015a-4167-b44b-0799a1a2605e"
 
 [compat]
 Documenter = "1"

docs/make.jl

@@ -1,5 +1,6 @@
 using Documenter
 using Graphs
+using NautyGraphs, IGraphs
 
 # same for contributing and license
 cp(

docs/src/ecosystem/graphalgorithms.md

@@ -2,7 +2,7 @@
 
 ## Defined by Graphs.jl
 
-_Graphs.jl_ provides a number of graph algorithms, including [Cuts](@ref), [Cycles](@ref), and [Trees](@ref), among many others. All algorithms work on any graph type that conforms to the _Graphs.jl_ API.
+_Graphs.jl_ provides a number of graph algorithms, including [Cuts](@ref), [Cycles](@ref), and [Trees](@ref), among many others. The algorithms work on any graph type that conforms to the _Graphs.jl_ API.
 
 ## External algorithm packages
 
@@ -15,7 +15,44 @@ Several other packages implement additional graph algorithms:
 
 ## Interfaces to other graph libraries
 
-Several packages make established graph libraries written in other languages accessible from within Julia and the Graphs.jl ecosystem:
+Several packages make established graph libraries written in other languages accessible from within Julia and the _Graphs.jl_ ecosystem:
 
 - [IGraphs.jl](https://github.com/JuliaGraphs/IGraphs.jl) is a thin Julia wrapper around the C graphs library [igraph](https://igraph.org).
-- [NautyGraphs.jl](https://github.com/JuliaGraphs/NautyGraphs.jl) provides graph structures compatible with the graph isomorphism library [_nauty_](https://pallini.di.uniroma1.it), allowing for efficient isomorphism checking and canonization, as well as computing the properties of graph automorphism groups.
+- [NautyGraphs.jl](https://github.com/JuliaGraphs/NautyGraphs.jl) provides graph structures compatible with the graph isomorphism library [_nauty_](https://pallini.di.uniroma1.it), allowing for efficient isomorphism checking and canonization, as well as computing the properties of graph automorphism groups.
+
+
+## Dispatching to algorithm implementations in external packages
+
+Apart from providing additional graph types and algorithms, many packages extend existing functions in _Graphs.jl_ with new backends. This can make it easier to use the additional algorithms from within _Graphs.jl_.
+
+For example, _NautyGraphs.jl_ provides a new backend for graph isomorphism calculations:
+
+```jldoctest
+julia> using Graphs, NautyGraphs
+
+julia> g = star_graph(5)
+{5, 4} undirected simple Int64 graph
+
+julia> Graphs.Experimental.has_isomorph(g, g, NautyAlg())
+true
+```
+
+Here, dispatching via `NautyAlg()` implicitly converts `g` to a _nauty_-compatible format and uses _nauty_ for the isomorphism computation.
+
+### Functions extended by IGraphs.jl
+
+A list of functions extended by _IGraphs.jl_ can be obtained with
+
+```@example
+using IGraphs
+IGraphs.igraphalg_methods()
+```
+
+### Functions extended by NautyGraphs.jl
+
+A list of functions extended by _NautyGraphs.jl_ can be obtained with
+
+```@example
+using NautyGraphs
+NautyGraphs.nautyalg_methods()
+```