S3 Update

docs/howto/s3_file_storage.rst

@@ -10,6 +10,36 @@ You can get access, browse and download files using your browser, using this lin
 **The LOGIN and PASSWORD for read access are available for all members** (but can't be published at open places like this site). Please ask on 
 `#software-helpdesk Slack channel <https://eicip6.slack.com/archives/C02267ZDARF>`_ or email one of the SWG members. 
 
+One can access S3 directly using TFile like this
+
+.. code:: C++
+
+    TFile* file = TFile::Open("s3https://dtn01.sdcc.bnl.gov:9000/eictest/ATHENA/<path>.root","AUTH=<login>:<password>");
+
+Or set environment variables `S3_ACCESS_KEY` and `S3_SECRET_KEY` instead of using AUTH and putting login and password to code;
+
+.. code:: bash
+
+    export S3_ACCESS_KEY=<login> 
+    export S3_SECRET_KEY=<password>
+
+
+XRootD access
+-------------
+
+One can utilize XRootD server to get access to files without credentials using: 
+
+.. code:: 
+
+    root://sci-xrootd.jlab.org//osgpool/eic/ATHENA/<path to file>
+
+.. code:: c++
+
+    std::string fileName = "RECO/JETS/crossDivNrgCrab/DIS_NC_Q2gt10_crossDivNrgCrab_25mRad_18x275_v1.0001.root";
+    TFile* file = TFile::Open("root://sci-xrootd.jlab.org//osgpool/eic/ATHENA/" + fileName);
+    // ...
+
+
 
 Installation
 ------------