Added documentation for Armstrong Number + Typo fix in Trie.md in /en

[SpiderMath]

Description

This pull request adds documentation for the algorithm for checking if a number is an Armstrong Number, the link to the entry is here. I plan to add further documentation for other entries but I am starting with low hanging fruit for now.

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)

None in this case

Note to reviewers

I'm rather unsure about the quality of my pseudocode, I feel it may be too spammy with comments or code-like to be pseudocode. Please review that bit. And the codespell action fails due to a typo in a completely different file I didn't touch, hence I haven't touched it in this case. I corrected the typo in question, in /en/Data Structures/Tries/trie.md

[SpiderMath]

Considering that the codespell is failing due to trie.md, I fixed it (revelant to relevant) and I've edited the title accordingly.