Implicit dependencies document added

Author: dehesa

docs/Dependencies.md

@@ -0,0 +1,19 @@
+# Implicit dependencies
+
+`CodableCSV` depends implicitly on the Swift Standard Library and `Foundation`. The `Foundation` types used throughout the library are:
+
+|      Name      |iOS|macOS|tvOS|watchOS|
+|----------------|---|-----|----|-------|
+|`Calendar`      |7  |10.9 |9   |2      |
+|`CharacterSet`  |7  |10.9 |9   |2      |
+|`CustomNSError` |7  |10.9 |9   |2      |
+|`Data`          |7  |10.9 |9   |2      |
+|`Date`          |7  |10.9 |9   |2      |
+|`DateFormatter` |2  |10.0 |9   |2      |
+|`Decimal`       |2  |10.0 |9   |2      |
+|`InputStream`   |2  |10.3 |9   |2      |
+|`Locale`        |7  |10.9 |9   |2      |
+|`LocalizedError`|7  |10.9 |9   |2      |
+|`OutputStream`  |2  |10.3 |9   |2      |
+|`TimeZone`      |7  |10.9 |9   |2      |
+|`URL`           |7  |10.9 |9   |2      |