Add some documentation on wildcard limitations in queries

The logstash UI will return hits on wildcarded queries but the
ElasticSearch configuration by default disables wildcard analysis so
queries in elastic-recheck with wildcards currently do not work, so
let's make sure this is documented in the readme.

Related-Bug: #1266833

Change-Id: If6b9d99d7ba83272fc8b735ab9e67fe1ee993811
Merge "Add some documentation on wildcard limitations in queries"