doc: samples: philosophers: Clean up README

[kartben]

before: https://docs.zephyrproject.org/latest/samples/philosophers/README.html
after: https://builds.zephyrproject.io/zephyr/pr/72878/docs/samples/philosophers/README.html

[aescolar]

Thanks.
Sidenote: I'm thinking we should not reformat lines from 80 to 100 chars, otherwise we are going to be changing a lot of lines.

[kartben]

Thanks. Sidenote: I'm thinking we should not reformat lines from 80 to 100 chars, otherwise we are going to be changing a lot of lines.

Ya I tend to agree but my thinking here was that the file was already inconsistent, with some sections already going past 80.
In fact, if we were to implement a change, I think I'd like to see us use a no line wrap policy, and rather have do one sentence/one line. This way, diffs are much cleaner when e.g one just adds a few words to a sentence, only that one line is changed as opposed to potentially many as everything in the paragraph gets "pushed".