added short Security section to readme

README.md

@@ -13,3 +13,11 @@ and [Network In Network (Lin et al., 2014)](https://arxiv.org/abs/1312.4400).
 
 * Install __proj__ on your machine using the console. E.g. for opensuse / leap `zypper install proj`
 * c++ compiler required for cartopy installation
+
+# Security
+
+* To use hourly data from ToarDB via JOIN interface, a private token is required. Request your personal access token and
+add it to `src/join_settings.py` in the hourly data section. Replace the `TOAR_SERVICE_URL` and the `Authorization` 
+value. To make sure, that this **sensitive** data is not uploaded to the remote server, use the following command to
+prevent git from tracking this file: `git update-index --assume-unchanged src/join_settings.py
+`
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