Add docs section on supported versions

Add section in the contributing docs about which version of Node.js and
Factorio is supported.

[skip travis]

docs/contributing.md

@@ -16,6 +16,7 @@ Contents
     - [Resolving Merge Conflicts](#resolving-merge-conflicts)
     - [Updating Your GitHub Fork](#updating-your-github-fork)
 - [Changelog](#changelog)
+- [Supported Node.js and Factorio Version](#supported-node.js-and-factorio-version)
 - [Code Style](#code-style)
     - [Indenting](#indenting)
     - [Line Length](#line-length)
@@ -155,6 +156,22 @@ add an entry to the changelog describing what has changed.  The format
 of this log should be self explanatory, please follow it carefully.
 
 
+Supported Node.js and Factorio Versions
+---------------------------------------
+
+Clusterio run on Node.js v12 and up, v11.13.0+ and v10.16.0+, make sure
+to check that the Node builtin API's and npm packages you use are
+supported on these versions.  The Travis CI tests are runned on whatever
+version of Node.js v10 is the default, which at the time of writing is
+v10.18.0.
+
+For Factorio Clusterio 2.0 aims to support version 0.17.69 and up,
+including the latest experimental release.  It's recommended that you
+use the lua API reference for 0.17.69, as there's no information on what
+version Factorio API's were introduced in.  The Travis CI tests are
+runned against latest experimental release.
+
+
 Code Style
 ----------