Update active branches for 3.0 release

Author: tbarsballe

CONTRIBUTING.md

@@ -26,8 +26,8 @@ project, but should be retired when a new release becomes more formalized.  Upon
 all content is expected to be folded into package documentation as appropriate (announcements,
 company blog posts, changelogs, migration guides, etc.).
 
-When a new major release is ready, the development mainline branch will be renamed to `main`, and the
-old mainline branch will be renamed to `maint-X.0` and will be used as the base for maintenance releases.
+When a new major release is ready, the old mainline branch will be copied to `maint-X.x` (e.g. `maint-2.x`), 
+to be used as the base for maintenance releases, and the development mainline branch will be merged into to `main`
 
 #### Development Branches
 

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     | `development` | [`main-3.0-dev`](https://github.com/planetlabs/planet-client-python/tree/main-3.0-dev) | [Planet Labs Python Client on ReadTheDocs.io](https://planet-sdk-for-python.readthedocs.io/en/latest/)       | Targeting August 2025 | TBD                       | TBD                | See [3.0.0 Release Milestone](https://github.com/planetlabs/planet-client-python/milestone/31). |
-| 2.x     | `active`      | [`main`](https://github.com/planetlabs/planet-client-python/tree/main)                 | [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)           | 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                |                                                                                                                              |
 
 ## Installation and Quick Start