Update creating-codeql-databases.rst

Author: esbena

docs/codeql/codeql-cli/creating-codeql-databases.rst

@@ -116,6 +116,8 @@ Here, we have specified a ``--source-root`` path, which is the location where
 database creation is executed, but is not necessarily the checkout root of the
 codebase. 
 
+By default, files in ``node_modules`` and ``bower_components`` directories are not extracted.
+
 Python
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