curl: add 2 options to -h important

[jhauga]

Summary

This PR adds 2 options to the important help category. Documentation is consistently voted 1 in the "Worst Areas" portion of the annual survey. And this pasts year one user made a suggestion to improve --help in regards to frequently used options, which this PR addresses.

1. curl 2025 Survey

In the section "Worst areas" the top pick was documentation at 28.3%, near 10% above the second in line. This PR will hopefully bring the down a few points.

See curl 2025 survey[1]

2. curl 2025 Survey

In the section "Which curl command line option do you think needs improvement and how?" one user wrote:

--help: it’d be a bit more convenient if it had a few more of the most frequently used flags rather than needing to remember to do --help all or man curl.

See curl 2025 survey [2]

This PR addresses the suggestion, adding 2 frequently used options.

Determining Options

Using the curl.se tutorial, curl-cheat-sheet repo, and 3 selected external tutorials; the options were selected if all pages included the option, and option deemed fitting. The selected external tutorials were:

• top 10 curl command
• Popular curl Examples
• Popular Curl -flags with short descriptions

Options Added

 -I, --head                              Show document info only
 -H, --header <header/@file>             Pass custom header(s) to server

[dfandrich]

-X, --request <method> Specify request method to use

Without even looking at the rest of the PR, this is definitely one option to leave out of the list. It is hardly ever needed and when it's used, it's almost always wrong. See https://daniel.haxx.se/blog/2015/09/11/unnecessary-use-of-curl-x/

[bagder]

Thanks!