Add Virtual memory caveats

On Linux the Virtual Memory settings might need to be changed. See this link for more details:
https://www.elastic.co/guide/en/elasticsearch/reference/current/vm-max-map-count.html

Change-Id: Id373f95d8e4d6a7463b736f4f5cb54dc12525b6b

README.md

diff --git a/README.md b/README.md
index 1eb971c..ade66a3 100644
--- a/README.md
+++ b/README.md
@@ -74,4 +74,11 @@
 
 This will compile, test and package the plugin artifact, which can be found in `./target/scala-2.11/analytics-wizard.jar`.
 
+# Caveats
 
+* **Virtual Memory settings**: run `sysctl -w vm.max_map_count=262144` from command line, if you are using a Linux box
+and the dashboard creation fails with a similar error:
+
+```bash
+max virtual memory areas vm.max_map_count [XXXXX] is too low, increase to at least [262144]
+```
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