docs(config): add parallelism option (#1509)

Add details for parallelism on the index and __Other Options__ page, with a 
note that profiling should be used.

Author: sokra

content/configuration/index.md

@@ -390,6 +390,9 @@ module.exports = {
 
   [resolveLoader](/configuration/resolve#resolveloader): { /* same as resolve */ }
   // separate resolve options for loaders
+  
+  [parallelism](other-options#parallelism): 1, // number
+  // limit the number of parallel processed modules
 
   [profile](other-options#profile): true, // boolean
   // capture timing information

content/configuration/other-options.md

@@ -84,6 +84,13 @@ Expose custom values into the loader context.
 ?> Add an example...
 
 
+## `parallelism`
+
+`number`
+
+Limit the number of parallel processed modules. Can be used to fine tune performance or to get more reliable profiling results.
+
+
 ## `profile`
 
 `boolean`
@@ -92,6 +99,8 @@ Capture a "profile" of the application, including statistics and hints, which ca
 
 T> Use the [StatsPlugin](https://www.npmjs.com/package/stats-webpack-plugin) for more control over the generated profile.
 
+T> Combine with `parallelism: 1` for better results.
+
 
 ## `recordsPath`