docs: concurrentRequestLimit and hostType (#17713)

docs/usage/configuration-options.md

@@ -1139,13 +1139,16 @@ Example config:
 {
   "hostRules": [
     {
-      "matchHost": "github.com",
+      "matchHost": "api.github.com",
       "concurrentRequestLimit": 2
     }
   ]
 }
 ```
 
+Use an exact host for `matchHost` and not a domain (e.g. `api.github.com` as shown above and not `github.com`).
+Do not combine with `hostType` in the same rule or it won't work.
+
 ### dnsCache
 
 Enable got [dnsCache](https://github.com/sindresorhus/got/blob/v11.5.2/readme.md#dnsCache) support.