Add exercise timing

[jcohen02]

This PR adds exercise timing to the episodes that include exercises but didn't have exercise timing set previously.

For "Examples of Using Container Images in Practice" (docker-image-examples.md), there are no specific exercise callouts but the content suggests choosing one or more of the provided examples to practice using containers. I've therefore cut the "teaching" time to 10 minutes, assuming that the instructor will provide a brief overview of the different examples, and added 15 minutes exercise time. Perhaps it would even be better to increase this to 20 or 25 minutes? This is flexible since it depends on how much time the instructor wants to dedicate to this.

Closes #232.

[github-actions]

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Rendered Changes

🔍 Inspect the changes: https://github.com/carpentries-incubator/docker-introduction/compare/md-outputs..md-outputs-PR-240

The following changes were observed in the rendered markdown documents:

 docker-image-examples.md | 4 ++--
 introduction.md          | 2 +-
 md5sum.txt               | 8 ++++----
 meet-docker.md           | 2 +-
 reproduciblity.md        | 2 +-
 5 files changed, 9 insertions(+), 9 deletions(-)

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If you have source files that require output and figures to be generated (e.g. R Markdown), then it is important to make sure the generated figures and output are reproducible.

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⏱️ Updated at 2024-07-31 18:50:07 +0000

[aturner-epcc]

LGTM