Refactor Node.gitignore with comments

The "build" directory is lost in this refactor, as many JS projects
do wish to include a minified/concatenated version of their source
in the "build" folder in source control.

Node.gitignore

@@ -1,15 +1,28 @@
-lib-cov
-*.seed
+# Semi-general patterns
+
+## Logs
+logs
 *.log
+
+## Runtime data
+pids
+*.pid
+*.seed
+
+## Run / build output
+results
 *.csv
 *.dat
 *.out
-*.pid
 *.gz
 
-pids
-logs
-results
-build
+# JS-specific patterns
+
+## Directory for files generated by jscoverage/JSCover
+lib-cov
+
+# Node-specific patterns
 
+## You may want to comment this out in certain scenarios:
+## see http://www.futurealoof.com/posts/nodemodules-in-git.html
 node_modules