Update version doc links, including new 'maint' link

Author: tbarsballe

README.md

@@ -82,11 +82,11 @@ See [CONTRIBUTING.md](CONTRIBUTING.md#branches) for more information on branches
 
 ##### Current Mainline Versions and Branches
 
-| Version | Status        | Branch                                                                           | Documentation                                                                                                | Initial Release | End of Active Development | End of Maintenance | Notes                                                                                                                        |
-|---------|---------------|----------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------|-----------------|---------------------------|--------------------|------------------------------------------------------------------------------------------------------------------------------|
-| 3.x     | `active`      | [`main`](https://github.com/planetlabs/planet-client-python/tree/main)           | TBD                                                                                                          | TBD             | TBD                       | TBD                | See [RELEASE-PLANNING-X.0.md](https://github.com/planetlabs/planet-client-python/tree/main-3.0-dev/RELEASE-PLANNING-3.0.md). |
-| 2.x     | `maintenance` | [`maint-2.x`](https://github.com/planetlabs/planet-client-python/tree/maint-2.x) | [Planet Labs Python Client v2 on Readthedocs.io](https://planet-sdk-for-python-v2.readthedocs.io/en/latest/) | April 2023      | TBD                       | TBD                |                                                                                                                              |
-| 1.x     | `end-of-life` | [`v1`](https://github.com/planetlabs/planet-client-python/tree/v1)               | [Planet Labs Python Client v1 on Github.io](https://planetlabs.github.io/planet-client-python/)              | April 2017      | April 2023                | TBD                |                                                                                                                              |
+| Version | Status        | Branch                                                                           | Documentation                                                                                                | Initial Release | End of Active Development | End of Maintenance | Notes |
+|---------|---------------|----------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------|-----------------|---------------------------|--------------------|-------|
+| 3.x     | `active`      | [`main`](https://github.com/planetlabs/planet-client-python/tree/main)           | [Planet Labs Python Client on Readthedocs.io](https://planet-sdk-for-python.readthedocs.io/en/stable/)       | August 2025     | TBD                       | TBD                |       |
+| 2.x     | `maintenance` | [`maint-2.x`](https://github.com/planetlabs/planet-client-python/tree/maint-2.x) | [Planet Labs Python Client 2.23.1 on Readthedocs.io](https://planet-sdk-for-python.readthedocs.io/en/maint/) | April 2023      | August 2025               | TBD                |       |
+| 1.x     | `end-of-life` | [`v1`](https://github.com/planetlabs/planet-client-python/tree/v1)               | [Planet Labs Python Client v1 on Github.io](https://planetlabs.github.io/planet-client-python/)              | April 2017      | April 2023                | TBD                |       |
 
 ## Installation and Quick Start