Cleanup what-is: better planning category

[rinkug]

EB member: @curfman

The original text for this what-is document seems to be solely focussing on texting and a bit on sustainability. I believe this was a copy-paste from some other file. Making this more suitable for this topic.

Partly Resolves #1598

PR checklist for files displayed on bssw.io site

• [Author] @mention the BSSw.io editorial board member @<eb-member-id> in Description above assigned to shepherd your PR.
• [Author] Add the <issue-id> in the Description above for the associated GitHub Issue.
• [ ] [Author] Ensure wikize_refs.py -i <base>.md is run and commit (if using [wikize_refs.py]).
• [Author] Inspect the content in the *.md file(s) as rendered in GitHub for this PR.
• [EB Mem] Assign this PR to the EB member <eb-member-id>.
• [EB Mem] Assign this PR to the author of the PR <pr-author-id>.
• [EB Mem] Add one or more Reviewers.
• [EB Mem] Add label content: <content-type> for the type of contribution.
• [EB Mem] Add to Project Content Development (see [Content Development]).
• [EB Mem] Add [meta-data] to the *.md file(s) (set Publish: yes).
• [EB Mem] Add label preview (so PR branch will be merged to 'preview' branch and watch for possible merge failures).
• [EB Mem] Rebuild [preview] site and confirm new content is there, renders correctly and is returned in searches.
• [Author] Make any final changes to the PR based on feedback.
• [ ] [Author] Ensure wikize_refs.py -i <base>.md is run and commit (if using [wikize_refs.py]).
• [EB Mem] Rebuild [preview] site and re-confirm content looks correct.
• [EB Mem] Ensure at least one reviewer signs off on the final changes.
• [EB Mem] Move the PR to "Ready to Publish" in [Content Development].
• [EB Mem] Leave comment and @mention @betterscientificsoftware/bssw-maint (BSSw Maint) asking to carry out final publication steps.
• [BSSw Maint] Verify that all needed files are present in the PR (article, images, updates to Site/Homepage.md carousel and/or Site/Announcements/Announcements.md as appropriate).
• [BSSw Maint] Merge PR. (Should automatically move to "Done" in [Content Development].)
• [BSSw Maint] Verify new contribution shows up on [bssw.io] as expected.