[DOCS] Add info about external lib

README.md

-t3o membership
-==============
-
-     
-
-What does it do?
-----------------
+# t3o membership
+   
+## What does it do?
 
 This extension imports our members from dropbox and displays at the 
 memberlisting at the Assocation page.
 
-
-Import Settings
----------------
+## Import Settings
 
 Installation:
 * Set up a scheduler task of type membership import
@@ -20,8 +14,12 @@ Installation:
   * CSV file to import (path and filename): Full path to the location where the memeber file should be stored. The folder should be secured via .htaccess
   * Dropbox Token: Token for accessing the dropbox folder
 
-
 The expected location within dropbox is:
 /TYPO3 Backoffice/Member-Lists/memberlist.txt
 
 The file is endocded with: ISO-8859-15
+
+## External libs
+
+This extension uses Dropbox-v2-PHP-SDK from lukeb2014, see:
+https://github.com/lukeb2014/Dropbox-v2-PHP-SDK