Add hint to allocate more memory if Elasticsearch crashes

[alxhu-dev]

When creating Elasticsearch indicies, the process might crash if there is not enough memory allocated to the JVM runtime.

This commit adds a hint (and a step-by-step-guide) for administrators to try to allocate more memory to Elasticsearch if they're experiencing out-of-memory issues.

(I had a hard time troubleshooting this issue and I think others could benefit from this solution.)

Feedback and suggestions for improvement are welcome.