add readme comment regarding the linux vm memory count issue

README.md

@@ -26,8 +26,17 @@ This is the preferred and fastest way to get the elastic index locally.<br/>
 The index on Docker Hub is updated with beginning of 2018 wikipedia dump.<br/>
 
 #### Docker Prerequisites
-Before starting this one-time process, make sure docker disk image size (*in your Docker Engine Preferences*) is not limited under 150GB.
+1) Before starting this one-time process, make sure docker disk image size (*in your Docker Engine Preferences*) is not limited under 150GB.
 Once below one-time process done, you can decrease image size
+2) If working with a Linux host, you might need to increase host vm.max_map_count,
+in order to verify you have the right value (i.e 262144), run: 
+
+        $>sudo sysctl vm.max_map_count
+        You should see: vm.max_map_count = 262144
+        If you see instead: vm.max_map_count = 65530, 
+        Fix by running:
+        $>sudo sysctl -w vm.max_map_count=262144
+
 
 #### Get Image and Build Container