Mention different Solr core path example in INSTALL.md

In current INSTALL.md file we see those example paths of Solr core:

mkdir $SOLR/server/solr/$CORE
mkdir $SOLR/server/solr/$CORE/conf
echo "name=$CORE" > $SOLR/server/solr/$CORE/core.properties

But in most Solr instances core files are located not in server/solr folder (because often this is read-only folder for solr user with Solr distributive files), but in something like /var/solr/data - not? Only in Docker-like system core files are placed together with system files, in server/solr folder.

So, maybe fix this discrepancy and place more popular place for core data location? Or describe both variants, including /var/solr/data?