Documentation/git-bundle.txt: mention full backup example

Provide an example about how to make a “full backup” with caveats about
what that means in this case.

This is a requested use-case.[1]  But the doc is a bit unassuming
about it:

    If you want to match `git clone --mirror`, which would include your
    refs such as `refs/remotes/*`, use `--all`.

The user cannot be expected to formulate “I want a full backup” as “I
want to match `git clone --mirror`” for a bundle file or something.
Let’s drop this mention of `--all` later in the doc and frontload it.

† 1: E.g.:

    • https://stackoverflow.com/questions/5578270/fully-backup-a-git-repo
    • https://stackoverflow.com/questions/11792671/how-to-git-bundle-a-complete-repo

Helped-by: Junio C Hamano <[email protected]>
Signed-off-by: Kristoffer Haugsbakk <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: LemmingAvalanche

Documentation/git-bundle.txt

@@ -23,8 +23,9 @@ the "offline" transfer of Git objects without an active "server"
 sitting on the other side of the network connection.
 
 They can be used to create both incremental and full backups of a
-repository, and to relay the state of the references in one repository
-to another.
+repository (see the "full backup" example in "EXAMPLES"), and to relay
+the state of the references in one repository to another (see the second
+example).
 
 Git commands that fetch or otherwise "read" via protocols such as
 `ssh://` and `https://` can also operate on bundle files. It is
@@ -34,8 +35,6 @@ contained within it with linkgit:git-ls-remote[1]. There's no
 corresponding "write" support, i.e.a 'git push' into a bundle is not
 supported.
 
-See the "EXAMPLES" section below for examples of how to use bundles.
-
 BUNDLE FORMAT
 -------------
 
@@ -216,8 +215,27 @@ bundle.
 EXAMPLES
 --------
 
-Assume you want to transfer the history from a repository R1 on machine A
-to another repository R2 on machine B.
+We'll discuss two cases:
+
+1. Taking a full backup of a repository
+2. Transfer the history of a repository to another machine when the two
+   machines have no direct connection
+
+First let's consider a full backup of the repository.  The following
+command will take a full backup of the repository in the sense that all
+refs are included in the bundle (except `refs/stash`, i.e. the stash):
+
+----------------
+$ git bundle create <file> --all
+----------------
+
+But note again that this is only for the refs, i.e. you will only
+include refs and commits reachable from those refs.  You will not
+include other local state, such as the contents of the index, working
+tree, per-repository configuration, hooks, etc.
+
+For the next example, assume you want to transfer the history from a
+repository R1 on machine A to another repository R2 on machine B.
 For whatever reason, direct connection between A and B is not allowed,
 but we can move data from A to B via some mechanism (CD, email, etc.).
 We want to update R2 with development made on the branch master in R1.