Clarify README about supported versions (post v7 release) (#7193)

Author: akx

README.md

@@ -12,13 +12,12 @@ computing.
 
 ## Maintained versions
 
-We maintain the **two most recently released major versions of Jupyter Notebook**, Notebook v5 and Classic Notebook v6. After Notebook v7.0 is released, we will no longer maintain Notebook v5. All Notebook v5 users are strongly advised to upgrade to Classic Notebook v6 as soon as possible.
+We maintain the **two most recently released major versions of Jupyter Notebook**,
+Classic Notebook v6 and Notebook v7. Notebook v5 is no longer maintained.
+All Notebook v5 users are strongly advised to upgrade to Classic Notebook v6 as soon as possible.
 
-The Jupyter Notebook project is currently undertaking a transition to a more modern code base built from the ground-up using JupyterLab components and extensions.
-
-There is new stream of work which was submitted and then accepted as a Jupyter Enhancement Proposal (JEP) as part of the next version (v7): https://jupyter.org/enhancement-proposals/79-notebook-v7/notebook-v7.html
-
-There is also a plan to continue maintaining Notebook v6 with bug and security fixes only, to ease the transition to Notebook v7: https://github.com/jupyter/notebook-team-compass/issues/5#issuecomment-1085254000
+Upgrading to Notebook v7 may require more work, if you use custom extensions, as extensions written
+for Notebook v5 or Classic Notebook v6 are not compatible with Notebook v7.
 
 ### Notebook v7
 
@@ -33,9 +32,8 @@ To learn more about Notebook v7: https://jupyter.org/enhancement-proposals/79-no
 
 ### Classic Notebook v6
 
-Maintenance and security-related issues are now being addressed in the [`6.4.x`](https://github.com/jupyter/notebook/tree/6.4.x) branch.
-
-A `6.5.x` branch will be soon created and will depend on [`nbclassic`](https://github.com/jupyter/nbclassic) for the HTML/JavaScript/CSS assets.
+Maintenance and security-related issues [only](https://github.com/jupyter/notebook-team-compass/issues/5#issuecomment-1085254000) are now being addressed in the [`6.5.x`](https://github.com/jupyter/notebook/tree/6.5.x) branch.
+It depends on [`nbclassic`](https://github.com/jupyter/nbclassic) for the HTML/JavaScript/CSS assets.
 
 New features and continuous improvement is now focused on Notebook v7 (see section above).