fsmonitor--daemon: man page

Create a manual page describing the `git fsmonitor--daemon` feature.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

Documentation/git-fsmonitor--daemon.txt

@@ -0,0 +1,75 @@
+git-fsmonitor--daemon(1)
+========================
+
+NAME
+----
+git-fsmonitor--daemon - A Built-in File System Monitor
+
+SYNOPSIS
+--------
+[verse]
+'git fsmonitor--daemon' start
+'git fsmonitor--daemon' run
+'git fsmonitor--daemon' stop
+'git fsmonitor--daemon' status
+
+DESCRIPTION
+-----------
+
+A daemon to watch the working directory for file and directory
+changes using platform-specific file system notification facilities.
+
+This daemon communicates directly with commands like `git status`
+using the link:technical/api-simple-ipc.html[simple IPC] interface
+instead of the slower linkgit:githooks[5] interface.
+
+This daemon is built into Git so that no third-party tools are
+required.
+
+OPTIONS
+-------
+
+start::
+	Starts a daemon in the background.
+
+run::
+	Runs a daemon in the foreground.
+
+stop::
+	Stops the daemon running in the current working
+	directory, if present.
+
+status::
+	Exits with zero status if a daemon is watching the
+	current working directory.
+
+REMARKS
+-------
+
+This daemon is a long running process used to watch a single working
+directory and maintain a list of the recently changed files and
+directories.  Performance of commands such as `git status` can be
+increased if they just ask for a summary of changes to the working
+directory and can avoid scanning the disk.
+
+When `core.useBuiltinFSMonitor` is set to `true` (see
+linkgit:git-config[1]) commands, such as `git status`, will ask the
+daemon for changes and automatically start it (if necessary).
+
+For more information see the "File System Monitor" section in
+linkgit:git-update-index[1].
+
+CAVEATS
+-------
+
+The fsmonitor daemon does not currently know about submodules and does
+not know to filter out file system events that happen within a
+submodule.  If fsmonitor daemon is watching a super repo and a file is
+modified within the working directory of a submodule, it will report
+the change (as happening against the super repo).  However, the client
+will properly ignore these extra events, so performance may be affected
+but it will not cause an incorrect result.
+
+GIT
+---
+Part of the linkgit:git[1] suite