[manifest] Proper desc, cleanup (#413)

the element is called desc. And should describe the image.

Also, assorted random trimming of excess precision...
You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/manifest/pull/413

-- Commit Summary --

  * Proper desc, cleanup

-- File Changes --

    M images/manifest-src-directive.svg (23)

-- Patch Links --

https://github.com/w3c/manifest/pull/413.patch
https://github.com/w3c/manifest/pull/413.diff

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/manifest/pull/413