docs: Small clarification on the usage of read_to_string and read_to_end trait methods

[kiseitai3]

Small clarification on the usage of read_to_string and read_to_end trait methods. The goal is to make it clear that these trait methods will become locked up if attempting to read to the end of stdin (which is a bit non-sensical unless the other end closes the pipe).

Fixes: #141714

[rustbot]

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[kiseitai3]

This is follow up work on #141935. If possible, reassign to @tgross35. A mistake was made in the previous PR. I attempted a rebase and one thing led to another and the branch became a mess, so I killed the branch. That autoclosed the old PR, so I opened a new one with changes more in line with what Trevor asked.

Sorry, but I hope this PR is more like what is expected in this project.

[tgross35]

If possible, reassign to @tgross35

I'll let you do this yourself for the experience :) you can request reviews by posting a comment, see rustbot's guidelines:

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[tgross35]

Also it looks like you accidentally picked up a submodule change here. There's about 1000 different ways to fix this but if you need a suggestion, I would do something like this:

# Reset to the point where your branch forked from `master`. The reset will get rid
# of your commit and mark all of the files as staged
git reset "$(git merge-base HEAD master)"

# Add the thing you care about
git add library/std

# Get ride of the unintentional changes
git restore src/doc

# Re-commit the files (now only what you care about) using 🪄 magic 🪄 to
# reuse the commit message you have now
git commit -C HEAD@{1}

# Update this PR
git push --force-with-lease

Also, you can always check exactly what your PR will look like before pushing with git diff "$(git merge-base HEAD master)", to avoid things like whatever bad luck you ran into with #141935 (comment).

(happy to help with git stuff if you have further questions)

[kiseitai3]

I'm not using git from the terminal. I am using it through RustRover and I assumed it had only picked up my modified file since I had not changed anything. However, I do see failure messages for what appear to be automatic attempts at running repository actions. I did not look closely since I have very little personal time for coding and I kinda wanted to move on with a milestone in my own personal project. I will need to correct that in my IDE settings. That's annoying.

I have used git in the terminal before so maybe that would have given me a clue. Maybe one of these days I will convert to Vim and embrace the terminal more (which is ironic considering I use the terminal 24/7 at work).

r? @tgross35

P.S. > Completely missed the docs changes getting picked up.