Explain .lock-wscript and move it

This changes the comment to better explain what .lock-wscript is for
(it's for the [obsolete][v0.8.0] node-waf build system), and moves it
next to the other ignore pattern(s) for binary module compilation artifacts.

[v0.8.0]: http://blog.nodejs.org/2012/06/25/node-v0-8-0/

Node.gitignore

@@ -16,6 +16,9 @@ coverage
 # Grunt intermediate storage (http://gruntjs.com/creating-plugins#storing-task-files)
 .grunt
 
+# node-waf configuration
+.lock-wscript
+
 # Compiled binary addons (http://nodejs.org/api/addons.html)
 build/Release
 
@@ -23,6 +26,3 @@ build/Release
 # Commenting this out is preferred by some people, see
 # https://www.npmjs.org/doc/misc/npm-faq.html#should-i-check-my-node_modules-folder-into-git-
 node_modules
-
-# Users Environment Variables
-.lock-wscript