Merge pull request #924 from kcormi/docs_lxplus9_temp

Add instructions for lxplus9

docs/index.md

@@ -134,6 +134,22 @@ make -j 4
 
 You will need to source `env_standalone.sh` each time you want to use the package, or add it to your login environment.
 
+##### Compilation on lxplus9
+
+For slc9 architectures, you will need to do the compilation in an slc7 environment using apptainer. You can then source the standalone script outside of the apptainer.
+On lxplus this can be done as follows:
+
+```
+git clone https://github.com/cms-analysis/HiggsAnalysis-CombinedLimit.git HiggsAnalysis/CombinedLimit
+cd HiggsAnalysis/CombinedLimit/ 
+# git checkout <some release>
+cmssw-el7
+. env_standalone.sh
+make -j 4
+exit
+source . env_standalone.sh
+```
+
 ##### Standalone compilation with LCG
 For compilation outside of CMSSW, for example to use ROOT versions not yet available in CMSSW, one can compile against LCG releases. The current default is to compile with LCG_102, which contains ROOT 6.26:
 ```sh