Feature 2751 release schedule

[jprestop]

This work had already been completed, but the development timeline had not been updated for the beta6 release, so I modified the instructions to help make it more clear and obvious. Please let me know if you have any suggested changes.

Pull Request Testing

• Describe testing already performed for these changes:
  

Reviewed the modified sections in Read the Docs:

• https://metplus.readthedocs.io/en/feature_2751_release_schedule/Release_Guide/metplus_development.html#update-release-notes

• https://metplus.readthedocs.io/en/feature_2751_release_schedule/Release_Guide/metplus_official.html#update-release-notes

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  

Review the instructions to ensure it is clear what needs to be done. Please also ensure that all tests pass.

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes or No]

• Do these changes include sufficient testing updates? [Yes]

• Will this PR result in changes to the test suite? [Yes or No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Do these changes introduce new SonarQube findings? [Yes]
  
  If yes, please describe:

• Please complete this pull request review by [20241111].
  

Pull Request Checklist

See the METplus Workflow for details.

• Add any new Python packages to the METplus Components Python Requirements table.
• For any new datasets, an entry to the METplus Verification Datasets Guide.
• Review the source issue metadata (required labels, projects, and milestone).
• Complete the PR definition above.
• Ensure the PR title matches the feature or bugfix branch name.
• Define the PR metadata, as permissions allow.
  Select: Reviewer(s) and Development issue
  Select: Milestone as the version that will include these changes
  Select: Coordinated METplus-X.Y Support project for bugfix releases or METplus-Wrappers-X.Y.Z Development project for official releases
• After submitting the PR, select the ⚙️ icon in the Development section of the right hand sidebar. Search for the issue that this PR will close and select it, if it is not already selected.
• After the PR is approved, merge your changes. If permissions do not allow this, request that the reviewer do the merge.
• Close the linked issue and delete your feature or bugfix branch from GitHub.

[georgemccabe]

Looks good!