data-aggregator: document "onwrite" fault model requirements

The *-onwrite.sh analysis scripts only work if import-trace was not
run with --no-write-ecs, i.e. they only work if writing memory
accesses were imported into the "trace" table.

Change-Id: Icb2ea4e72d2200c886d4f9074f2da0f9bfd6ac85

tools/analysis/data-aggregator/symbol-coverage-onwrite.sh

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+# TODO implement show_description
+
 source $(dirname $0)/fail-analysis-common.inc.sh
 
 $MYSQL << EOT