Update default shard count per index in readme (#42388)
Update default shard count per index in readme (#42388)

The default shard count has been reduced from 5 to 1. This commit
updates the readme to reflect that changed default.
gingerwizard/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,HonzaKral/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch,coding0011/elasticsearch,robin13/elasticsearch,nknize/elasticsearch,scorpionvicky/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,uschindler/elasticsearch,coding0011/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,scorpionvicky/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,uschindler/elasticsearch,HonzaKral/elasticsearch,gingerwizard/elasticsearch,robin13/elasticsearch,HonzaKral/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,scorpionvicky/elasticsearch,HonzaKral/elasticsearch,GlenRSmith/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,coding0011/elasticsearch,coding0011/elasticsearch,uschindler/elasticsearch