updated docs

README.md

@@ -121,6 +121,7 @@ request.env['ipinfo'].all ==
  In addition to the steps listed in the Installation section it is possible to configure the library with more detail. The following arguments are allowed and are described in detail below.
 
 ```ruby
+require 'ipinfo-rails/ipselector/xforwarded_ipselector'
 config.middleware.use(IPinfoMiddleware, {
   token: "<your_token>",
   ttl: "",
@@ -129,8 +130,31 @@ config.middleware.use(IPinfoMiddleware, {
   http_client: "",
   countries: "",
   filter: "",
+  ipselector: XForwardedIPSelector,
 })
 ```
+### IP Selection Mechanism
+
+By default, the IP is used by ignoring the reverse proxies depending on whether we are behind a reverse proxy or not.
+
+Since the desired IP by your system may be in other locations, the IP selection mechanism is configurable and some alternative built-in options are available.
+Using built-in IP selectors
+
+  - [DefaultIPSelector](./lib/ipinfo-rails/ipselector/default_ipselector.rb)
+  - [XForwardedIPSelector](./lib/ipinfo-rails/ipselector/xforwarded_ipselector.rb)
+
+#### Using a custom IP selector
+
+In case a custom IP selector is required, you may implement the `IPSelectorInterface` and pass the class to `ipselector` in config.
+```ruby
+require 'custom-package/custom_ipselector'
+config.middleware.use(IPinfoMiddleware, {
+  token: "<your_token>",
+  ipselector: CustomIPSelector,
+})
+```
+
+
 
 ### Authentication