docs(plugins): add ProfilingPlugin documentation (#1830)

Author: EugeneHlushko

src/content/plugins/profiling-plugin.md

@@ -0,0 +1,33 @@
+---
+title: ProfilingPlugin
+contributors:
+  - EugeneHlushko
+---
+
+Generate Chrome profile file which includes timings of plugins execution. Outputs `events.json` file by default. It is possible to provide custom file path using `outputPath` option.
+
+## Options
+
+- `outputPath`: A relative path to a custom output file (json)
+
+## Usage: default
+
+``` js
+new webpack.debug.ProfilingPlugin()
+```
+
+## Usage: custom `outputPath`
+
+``` js
+new webpack.debug.ProfilingPlugin({
+  outputPath: "profiling/profileEvents.json"
+})
+```
+
+In order to view the profile file:
+
+- Run webpack with `ProfilingPlugin`.
+- Go to Chrome, open the `Profile Tab`.
+- Drag and drop generated file (`events.json` by default) into the profiler.
+
+It will then display timeline stats and calls per plugin!