update README

README.md

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 # CombineHarvester
-CMSSW package for the creation, editing and analysis of combine datacards and workspaces
+
+Full documentation: http://cms-analysis.github.io/CombineHarvester
+
+## Quick start
+
+This pacakge requires HiggsAnalysis/CombinedLimit to be in your local CMSSW area. We follow the release recommendations of the combine developers which can be found [here](https://twiki.cern.ch/twiki/bin/viewauth/CMS/SWGuideHiggsAnalysisCombinedLimit#ROOT5_SLC6_release_CMSSW_7_1_X). Note that the CombineHarvester framework is only compatible with the CMSSW 7_X_Y series releases.  A new release area can be set up and compiled in the following steps:
+
+    export SCRAM_ARCH=slc6_amd64_gcc481
+    scram project CMSSW CMSSW_7_1_5
+    cd CMSSW_7_1_5/src
+    cmsenv
+    git clone https://github.com/cms-analysis/HiggsAnalysis-CombinedLimit.git HiggsAnalysis/CombinedLimit
+    git clone https://github.com/cms-analysis/CombineHarvester.git CombineHarvester
+    scram b
+
+**Important:** The CombineHarvester package currently requires the head of the default HiggsAnalysis/CombinedLimit branch (`slc6-root5.34.17`) and will not compile successfully with the tag listed on the combine twiki page. A new tag will be provided soon.
+