Add guidance around the number of sources a user should create (#4053)

* Update index.md

Add info block about whether customer should set up one source or multiple sources

* Update src/connections/sources/index.md

Co-authored-by: markzegarelli <mark.zegarelli@segment.com>

* Update src/connections/sources/index.md

Co-authored-by: markzegarelli <mark.zegarelli@segment.com>

* Update src/connections/sources/index.md

Co-authored-by: markzegarelli <mark.zegarelli@segment.com>

Co-authored-by: markzegarelli <mark.zegarelli@segment.com>

Author: sarahrudy

src/connections/sources/index.md

@@ -71,6 +71,12 @@ To create a source:
 4. Enter a name for your source as well as any information on the setup page.
 5. Click **Add Source**.
 
+> info "One source or multiple sources?"
+> Segment suggests that you create one source for each type of data you want to collect. For example, you might have one source for all of your website tracking and a different source for any mobile tracking. Creating one source per data type provides the following benefits:
+> - Debugger ease of use - mixing libraries/sources on a single API key means you’re heavily reliant on filtering to actually test events
+> - Flexibility sending data to different projects - if you want to have different warehouse schemas, analytics projects, etc, having multiple sources would create this separation
+> - More control - as your account grows with the number of destinations you enable, having separate sources allows you to have more control
+
 ## Website libraries
 
 [Analytics.js](/docs/connections/sources/catalog/libraries/website/javascript/), the JavaScript library, is the most powerful way to track customer data from your website. If you're just starting out, Segment recommends it over server-side libraries as the simplest installation for any website.