doc: git-pull: move <repository> and <refspec> params

From user feedback:

- it's confusing that we use both <branch> and <refspec> to refer to the
  second argument
- one user is not clear about what `refs/heads/*:refs/remotes/origin/*`
  is meant to be an example of ("is it like a path?")

The DESCRIPTION section is also doing a lot right now: it's trying to
describe both how the <repository> and <refspec> arguments work (which
is extremely complex, as seen in the DEFAULT BEHAVIOUR section)
as well as how `git pull` calls `git fetch` and merge/rebase/etc
depending on the arguments.

Handle this by moving the description of the <repository> and <refspec>
arguments to the OPTIONS section, so that we can focus on the
merge/rebase/etc behaviour in the DESCRIPTION section, and refer folks
to the later sections for details.

Use the term "upstream" instead of 'the "remote" and "merge"
configuration for the current branch' since users are more likely to
know what an "upstream" is.

Signed-off-by: Julia Evans <[email protected]>

Author: jvns

Documentation/git-pull.adoc

@@ -27,17 +27,6 @@ and then depending on configuration options or command line flags,
 will call either `git rebase` or `git merge` to reconcile diverging
 branches.
 
-<repository> should be the name of a remote repository as
-passed to linkgit:git-fetch[1].  <refspec> can name an
-arbitrary remote ref (for example, the name of a tag) or even
-a collection of refs with corresponding remote-tracking branches
-(e.g., refs/heads/{asterisk}:refs/remotes/origin/{asterisk}),
-but usually it is the name of a branch in the remote repository.
-
-Default values for <repository> and <branch> are read from the
-"remote" and "merge" configuration for the current branch
-as set by linkgit:git-branch[1] `--track`.
-
 Assume the following history exists and the current branch is
 "`master`":
 
@@ -77,6 +66,24 @@ pulling or stash them away with linkgit:git-stash[1].
 OPTIONS
 -------
 
+<repository>::
+	The "remote" repository to pull from.  This can be either
+	a URL (see the section <<URLS,GIT URLS>> below) or the name
+	of a remote (see the section <<REMOTES,REMOTES>> below).
++
+Defaults to the configured upstream for the current branch, or `origin`.
+See UPSTREAM BRANCHES below for more on how to configure upstreams.
+
+<refspec>::
+	Which branch or other reference(s) to fetch and integrate into the
+	current branch, for example `main` in `git pull origin main`.
+	Defaults to the configured upstream for the current branch.
++
+This can be a branch, tag, or other collection of reference(s).
+See <refspec> below under "Options related to fetching" for the full syntax,
+and DEFAULT BEHAVIOUR below for how `git pull` uses this argument to
+determine which remote branch to integrate.
+
 -q::
 --quiet::
 	This is passed to both underlying git-fetch to squelch reporting of