Added temporary notice on license change to readme.md (#18607)
Publicising the discussion on github for the GPL-2 license
harmonisation.
### Link to issue number:
https://github.com/nvaccess/nvda/discussions/18574
### Summary of the issue:
Community consultation on GPL-2 or later change.
### Description of user facing changes:
None
### Description of developer facing changes:
2-month inclusion of notice in README.md
### Description of development approach:
On 28 Sept, the notice will be removed.
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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
