added PBS config faq entries (#3340)

faq/prebid-server-faq.md

@@ -168,3 +168,37 @@ Another way is to [register for our host company mailing list](/prebid-server/ho
 Prebid Server is not a full-fledged SSP. Any DSP bid adapters should keep this in mind when it comes to assuming SSP functionality like resolving OpenRTB macros. We debated building this functionality into PBS, but realized it would take precious milliseconds away from the overall header bidding auction to scan kilobytes of bidder creatives for the 9 different OpenRTB macros. Since so few bidders require this functionality, it makes sense to have those adapters do it themselves.
 
 If an adapter doesn't resolve its own macros, AUCTION_PRICE will eventually get resolved by the [Prebid Universal Creative](https://github.com/prebid/prebid-universal-creative), but by then the bid price will be in the ad server currency and quantized by the price granularity. This will likely cause reporting discrepancies.
+
+## Does Prebid Server support region-specific endpoints for bidders?
+
+Yes. This is handled by the PBS host company in their datacenter config.
+Bidders that want to make use of region-specific endpoints will need to work
+with each PBS host company:
+
+- determine which regions the host company supports
+- map the regions to the bidder's endpoints
+- the host company overrides the bidder's default auction endpoint when they deploy the configuration for each region.
+
+We recognize that it's inconvenient for bidders to be required to have this
+conversation with each host company, but there's really not a better way
+in an open source project. Any number of companies may choose to host
+PBS and we cannot constrain them into a defined set of regions.
+
+## Can bidder endpoints differ by publisher?
+
+You may not use an endpoint domain as a bidder parameter. Prebid Server is not
+an open proxy. If absolutely necessary, you may specify a portion of the
+domain as a parameter to support geo regions or account specific servers.
+However, this is discouraged and may degrade the performance of your adapter
+since the server needs to maintain more outgoing connections. Host companies
+may choose to disable your adapter if it uses a dynamically configured domain.
+
+e.g. this config is not allowed because the entire domain name is a variable:
+
+```
+endpoint: "https://{host}/path"
+```
+but this would be ok:
+```
+endpoint: "https://{host}.example.com/path"
+```