Explain the use of double backslashes with regex (neo4j#2664)

This is the copy of the PR neo4j#2655

Author: NataliaIvakina

modules/ROOT/pages/tools/neo4j-admin/neo4j-admin-import.adoc

@@ -494,6 +494,13 @@ For example:
 bin/neo4j-admin database import full --nodes import/node_header.csv,import/node_data_\d+\.csv
 ----
 
+[NOTE]
+====
+In many scripting languages, you must use double backslashes (`\\`) when defining regular expression patterns inside string literals.
+This is because a single backslash (`\`) is treated as an escape character.
+====
+
+
 ==== Import data from CSV files using a more complex regular expression
 
 For regular expression patterns containing commas, which is also the delimiter between files in a group, the pattern can be quoted to preserve the pattern.