Add migration to v4 document into Guides section

[jeremenichelli]

Create a document to migrate to webpack v4 (legato).

The document should be in a new Migrations subsection from Guides page.

• Create Migrations Section - It contains both the existing content which should be labeled v2/3 [Dependency: Guides] - Create "Migrating" section and move content from Guides #1933

• Complete Migration v4 Guide - It should contain the v2/3 -> v4 Migration information [Dependency: Guides] - Add v4 Migration Guide #1934

• (Nice to have) - Add loader and plugin migration instructions in v4 Migration Guide [Dependency: Guides] - Add v4 Plugin and Loader Migration example - Place in Migrating/4 - Post MVP #1935

[benmonro]

dear universe please let this get worked on soon. 👍

[EugeneHlushko]

@jeremenichelli i would quesstion v2 -> v4 migration guide necessity. Lets maybe do v3 -> v4? I've tackled the first item and probably can pick up next after rebuild gets merged