[Whitelisting] Add new page

Whitelisting.md

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+RSS-Bridge supports whitelists in order to limit the available bridges on your web server. Once you have installed and accessed RSS-Bridge for the first time, a file named `whitelist.txt` will automatically be created in the root folder of RSS-Bridge.
+
+#Specific whitelisting
+
+In order to specifically whitelist bridges, open `whitelist.txt` and add one line for each bridge you want to show. Make sure you use normal [line-feeds](https://en.wikipedia.org/wiki/Newline "Line-feed") at the end of a line (LF not [CRLF](https://en.wikipedia.org/wiki/Carriage_return "Carriage-return line-feed")). The bridge name must match the filename of the bridge in the bridges folder (see [folder structure](Folder-structure)). The name may or may not include the 'Bridge' part.
+
+**Examples**:
+```TEXT
+FacebookBridge
+WikipediaBridge
+TwitterBridge
+```
+
+or
+
+```TEXT
+Facebook
+Wikipedia
+Twitter
+```
+
+#Global whitelisting
+
+In order to globally whitelist all bridges, open the `whitelist.txt` file, remove all contents and just write an asterisk `*` into the file (only this one character).
+
+```TEXT
+*
+```