configuration and docs for tracking exports

Not yet handled by sync or assistant.

This commit was sponsored by Nick Daly on Patreon.

doc/git-annex-export.mdwn

@@ -6,6 +6,8 @@ git-annex export - export content to a remote
 
 git annex export `treeish --to remote`
 
+git annex export `--tracking treeish --to remote`
+
 # DESCRIPTION
 
 Use this command to export a tree of files from a git-annex repository.
@@ -36,6 +38,18 @@ verification of content downloaded from an export. Some types of keys,
 that are not based on checksums, cannot be downloaded from an export.
 And, git-annex will never trust an export to retain the content of a key.
 
+# OPTIONS
+
+* `--to=remote`
+
+  Specify the special remote to export to.
+
+* `--tracking`
+
+  This makes the export track changes that are committed to
+  the branch. `git annex sync --content` and the git-annex assistant
+  will update exports when it commits to the branch they are tracking.
+
 # EXAMPLE
 
 	git annex initremote myexport type=directory directory=/mnt/myexport \
@@ -56,6 +70,10 @@ That updates /mnt/myexport to reflect the renamed file.
 That updates /mnt/myexport, to contain only the files in the "subdir"
 directory of the master branch.
 
+	git annex export --tracking master --to myexport
+
+That makes myexport track changes that are committed to the master branch.
+
 # EXPORT CONFLICTS
 
 If two different git-annex repositories are both exporting different trees
@@ -81,6 +99,8 @@ export`, it will detect the export conflict, and resolve it.
 
 [[git-annex-initremote]](1)
 
+[[git-annex-sync]](1)
+
 # AUTHOR
 
 Joey Hess <id@joeyh.name>

doc/git-annex-sync.mdwn

@@ -82,6 +82,10 @@ by running "git annex sync" on the remote.
   This behavior can be overridden by configuring the preferred content
   of a repository. See [[git-annex-preferred-content]](1).
 
+  When a special remote is configured as an export and is tracking a branch,
+  the export will be updated to the current content of the branch.
+  See [[git-annex-export]](1).
+
 * `--content-of=path` `-C path`
 
   While --content operates on all annexed files in the work tree,

doc/git-annex.mdwn

@@ -1210,6 +1210,14 @@ Here are all the supported configuration settings.
   from remotes. If you trust a remote and don't want the overhead
   of these checksums, you can set this to `false`.
 
+* `remote.<name>.annex-export-tracking`
+
+  When set to a branch name or other treeish, this makes what's exported
+  to the special remote track changes to the branch. See
+  [[git-annex-export]](1). `git-annex sync --content` and the 
+  git-annex assistant update exports when changes have been
+  committed to the tracking branch.
+
 * `remote.<name>.annexUrl`
 
   Can be used to specify a different url than the regular `remote.<name>.url`