Added editors section with known OpenAPI 3.0 Editors

Not sure if you want to include commercial tools, or just open source components.  If this is only for open source tooling, you can remove the RepreZen API Studio row from the table.  (Or comment on the PR, and I'll remove it.)

Author: tedepstein

IMPLEMENTATIONS.md

@@ -20,6 +20,15 @@ These tools are not necessarily endorsed by the OAI.
 | Tavis.OpenApi | [GitHub/tavis-sofware/Tavis.OpenApi](https://github.com/tavis-software/Tavis.OpenApi/) | dotnet | C# based parser with definition validation and migration support from V2 |
 
 
+#### Editors
+
+| Title          | Project Link | Language |Description                          |
+|----------------|--------------|----------|---------------------|
+| KaiZen OpenAPI Editor | [GitHub/RepreZen/KaiZen-OpenAPI-Editor](https://github.com/RepreZen/KaiZen-OpenAPI-Editor) | Java | Eclipse Editor for OpenAPI 2.0 and 3.0 |
+| RepreZen API Studio | [RepreZen.com/OpenAPI](https://www.reprezen.com/OpenAPI) | Java | Commercial desktop IDE for API design, documentation & development |
+| OpenApi-gui | [GitHub/Mermade/openapi-gui](https://github.com/Mermade/openapi-gui) | Node.js | GUI / visual editor for creating and editing OpenApi / Swagger definitions |
+
+
 #### User Interfaces
 
 | Title          | Project Link | Language |Description                          |