doc: git-pull: clarify options for integrating remote branch

From user feedback:

- One user is confused about the current default ("I was convinced that
  the git default was still to merge on pull")
- One user is confused about why "git fetch" isn't mentioned earlier
- One user says they always forget what the arguments to `git pull` are
  and that it's not immediately obvious that `--no-rebase` means "merge"
- One user wants `--ff-only` to be mentioned

Resolve this by listing the options for integrating the the remote
branch. This should help users figure out at a glance which one they
want to do, and make it clearer that --ff-only is the default.

Signed-off-by: Julia Evans <julia@jvns.ca>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: jvns

Documentation/git-pull.adoc

@@ -15,17 +15,26 @@ SYNOPSIS
 DESCRIPTION
 -----------
 
-Incorporates changes from a remote repository into the current branch.
-If the current branch is behind the remote, then by default it will
-fast-forward the current branch to match the remote.  If the current
-branch and the remote have diverged, the user needs to specify how to
-reconcile the divergent branches with `--rebase` or `--no-rebase` (or
-the corresponding configuration option in `pull.rebase`).
-
-More precisely, `git pull` runs `git fetch` with the given parameters
-and then depending on configuration options or command line flags,
-will call either `git rebase` or `git merge` to reconcile diverging
-branches.
+Integrate changes from a remote repository into the current branch.
+
+First, `git pull` runs `git fetch` with the same arguments
+(excluding merge options) to fetch remote branch(es).
+Then it decides which remote branch to integrate: if you run `git pull`
+with no arguments this defaults to the <<UPSTREAM-BRANCHES,upstream>>
+for the current branch.
+Then it integrates that branch into the current branch.
+
+There are 4 main options for integrating the remote branch:
+
+1. `git pull --ff-only` will only do "fast-forward" updates: it
+   fails if your local branch has diverged from the remote branch.
+   This is the default.
+2. `git pull --rebase` runs `git rebase`
+3. `git pull --no-rebase` runs `git merge`.
+4. `git pull --squash` runs `git merge --squash`
+
+You can also set the configuration options `pull.rebase`, `pull.squash`,
+or `pull.ff` with your preferred behaviour.
 
 Assume the following history exists and the current branch is
 "`master`":