Added explanation for Ceil

[SpiderMath]

Description

This pull request aims to add an algorithm explanation for Ceil. I'm aware that this is a small addition but I plan to add further, but I have been told in the past to add things one by one, hence I'm following those instructions. I've tried to be as concise yet understandable as possible, but I may have overcomplicated things a bit, please do check and let me know what sort of changes you may require me to make in this added documentation.

Checklist

• A description of the changes in this PR is mentioned above.
• All the new and existing checks pass.
• No plagiarized, duplicated, or repetitive documentation that has been directly copied from another source.
• If it's a new explanation, it contains solid, understandable, and accessible information.
• I have read the whole contributing guidelines and agree to the Code of Conduct.

Screenshots (if any)

Not applicable in this case.

Note to reviewers

Already stated in description!

[github-actions]

This pull request has been automatically marked as abandoned because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[github-actions]

Please ping one of the maintainers once you commit the changes requested or make improvements on the code. If this is not the case and you need some help, feel free to ask for help in our Gitter channel. Thank you for your contributions!