Clarify documentation about what constitutes a title in `--message`

It's not only the first line of text; it's the entire first "block" (or
paragraph) of text with newlines turned into spaces. This is for
compatibility with git-commit(1).

commands/issue.go

@@ -106,7 +106,8 @@ With no arguments, show a list of open issues.
 		%uI: updated date, ISO 8601 format
 
 	-m, --message <MESSAGE>
-		Use the first line of <MESSAGE> as issue title, and the rest as issue description.
+		The text up to the first blank line in <MESSAGE> is treated as the issue
+		title, and the rest is used as issue description in Markdown format.
 
 	-F, --file <FILE>
 		Read the issue title and description from <FILE>.

commands/pull_request.go

@@ -29,8 +29,9 @@ pull-request -i <ISSUE>
 		Skip the check for unpushed commits.
 
 	-m, --message <MESSAGE>
-		Use the first line of <MESSAGE> as pull request title, and the rest as pull
-		request description.
+		The text up to the first blank line in <MESSAGE> is treated as the pull
+		request title, and the rest is used as pull request description in Markdown
+		format.
 
 	--no-edit
 		Use the message from the first commit on the branch as pull request title

commands/release.go

@@ -73,7 +73,8 @@ With '--exclude-prereleases', exclude non-stable releases from the listing.
 		character is taken as asset label.
 
 	-m, --message <MESSAGE>
-		Use the first line of <MESSAGE> as release title, and the rest as release description.
+		The text up to the first blank line in <MESSAGE> is treated as the release
+		title, and the rest is used as release description in Markdown format.
 
 	-F, --file <FILE>
 		Read the release title and description from <FILE>.

etc/hub.fish_completion

@@ -34,7 +34,7 @@ complete -f -c hub -n '__fish_hub_needs_command' -a sync -d "update local branch
 complete -f -c hub -n ' __fish_hub_using_command alias' -a 'bash zsh sh ksh csh fish' -d "output shell script suitable for eval"
 # pull-request
 complete -f -c hub -n ' __fish_hub_using_command pull-request' -s f -d "Skip the check for unpushed commits"
-complete -f -c hub -n ' __fish_hub_using_command pull-request' -s -m -d "Use the first line of <MESSAGE> as pull request title, and the rest as pull request description"
+complete -f -c hub -n ' __fish_hub_using_command pull-request' -s -m -d "Set the pull request title and description separated by a blank line"
 complete -f -c hub -n ' __fish_hub_using_command pull-request' -s F -d "Read the pull request title and description from <FILE>"
 complete -f -c hub -n ' __fish_hub_using_command pull-request' -s o -d "Open the new pull request in a web browser"
 complete -f -c hub -n ' __fish_hub_using_command pull-request' -l browse -d "Open the new pull request in a web browser"