doc: add N-API version 6 to table

We missed adding version 6 to the compatibility
table when we defined version 6. Add it along with the
versions that we know will include version 6.

PR-URL: #32829
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gabriel Schulhof <gabriel.schulhof@intel.com>

Author: mhdawson

doc/api/n-api.md

@@ -241,15 +241,16 @@ from version 3 with some additions. This means that it is not necessary
 to recompile for new versions of Node.js which are
 listed as supporting a later version.
 
-|       | 1       | 2        | 3        | 4        | 5         |
-|-------|---------|----------|----------|----------|-----------|
-| v6.x  |         |          | v6.14.2* |          |           |
-| v8.x  | v8.0.0* | v8.10.0* | v8.11.2  | v8.16.0  |           |
-| v9.x  | v9.0.0* | v9.3.0*  | v9.11.0* |          |           |
-| v10.x | v10.0.0 | v10.0.0  | v10.0.0  | v10.16.0 | v10.17.0  |
-| v11.x | v11.0.0 | v11.0.0  | v11.0.0  | v11.8.0  |           |
-| v12.x | v12.0.0 | v12.0.0  | v12.0.0  | v12.0.0  | v12.11.0  |
-| v13.x | v13.0.0 | v13.0.0  | v13.0.0  | v13.0.0  | v13.0.0   |
+|       | 1       | 2        | 3        | 4        | 5         | 6         |
+|-------|---------|----------|----------|----------|-----------|-----------|
+| v6.x  |         |          | v6.14.2* |          |           |           |
+| v8.x  | v8.0.0* | v8.10.0* | v8.11.2  | v8.16.0  |           |           |
+| v9.x  | v9.0.0* | v9.3.0*  | v9.11.0* |          |           |           |
+| v10.x | v10.0.0 | v10.0.0  | v10.0.0  | v10.16.0 | v10.17.0  | v10.20.0  |
+| v11.x | v11.0.0 | v11.0.0  | v11.0.0  | v11.8.0  |           |           |
+| v12.x | v12.0.0 | v12.0.0  | v12.0.0  | v12.0.0  | v12.11.0  |           |
+| v13.x | v13.0.0 | v13.0.0  | v13.0.0  | v13.0.0  | v13.0.0   |           |
+| v14.x | v14.0.0 | v14.0.0  | v14.0.0  | v14.0.0  | v14.0.0   | v14.0.0   |
 
 \* Indicates that the N-API version was released as experimental