Merge branch 'patch-133' into 'master'

Added reseller marketing contents link.

As per [issue](https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/4124#note_19857388)

See merge request !4200

source/handbook/marketing/product-marketing/index.html.md

@@ -20,6 +20,7 @@ The Product Marketing organization includes Product Marketing, Content Marketing
 ## Product Marketing Handbooks  
 * [Content marketing](/handbook/marketing/product-marketing/content-marketing/)
 * [Partner marketing](/handbook/marketing/product-marketing/partner-marketing/)
+* [Reseller marketing](/handbook/marketing/product-marketing/reseller-marketing/)
 ## Key Responsibilities<a name="responsibilities"></a>