fix(doc): don't show the opening message when --path is used

[0x61nas]

This might seem like a travel or unnecessary thing, especially since the message is written to stderr so it won't affect piping or similar use cases.
But since stdout and stderr are ambiguous in most terminals (i.e., they're printed in the output) this might cause some confusion and/or annoyance to some users.

[rami3l]

LGTM!

Besides, your topic_name does remind me of an edge case that I forgot to handle in #3674: rustup doc std::fs.
Reusing this variable gives Opening docs named `std::fs` in your browser, I guess that looks just right?

[0x61nas]

LGTM!

Besides, your topic_name does remind me of an edge case that I forgot to handle in #3674: rustup doc std::fs. Reusing this variable gives Opening docs named `std::fs` in your browser, I guess that looks just right?

this edge case are still exists, when i try rustup doc std::fs it rising this message Opening docs in your browser, as if i didn't specify a topic, but still opens the correct page

sorry, i forget to run the init command, yup every thing seams to work fine now

[rami3l]

@0x61nas Thanks again!