Add prefer_extracted_top_level_constant analyzer comment to javascrip…

…t resistor color duo (exercism/javascript-analyzer#127)

analyzer-comments/javascript/resistor-color-duo/prefer_extracted_top_level_constant.md

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+# prefer extracted top level constant
+
+Consider extracting the constant to the top level scope:
+
+```javascript
+const %{name} = %{value}
+
+// the rest of your code below it
+export const decodedValue = (...)
+```
+
+Only functions, classes and constants that are `export`ed, are visible and
+accessible from the outside. These constants can live in the same
+file without being exposed to other code. Also, extracting constants saves memory 
+by avoiding repeated allocations in functions when those same constants are reused.