Add "User Guide" link to navigation bar

[SteveChapmanBCDX]

Dan Hirner's recent BCGW research indicated that our clients need an easier way to access the BC Data Catalogue User's Guide.

Let's add a new navigation link to the navigation bar.

Requirements:

• Label named "User Guide"
• Link to https://www2.gov.bc.ca/gov/content/data/bc-data-catalogue/bc-data-catalogue-about/bc-data-catalogue-user-guide