fsmonitor: mark the built-in FSMonitor as experimental

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Documentation/config/core.txt

@@ -71,7 +71,7 @@ git by avoiding unnecessary scanning of files that have not changed.
 +
 See the "fsmonitor-watchman" section of linkgit:githooks[5].
 +
-Note: The value of this config setting is ignored if the
+Note: The value of this config setting is ignored if the (experimental)
 built-in file system monitor is enabled (see `core.useBuiltinFSMonitor`).
 
 core.fsmonitorHookVersion::
@@ -91,7 +91,7 @@ Note: The value of this config setting is ignored if the
 built-in file system monitor is enabled (see `core.useBuiltinFSMonitor`).
 
 core.useBuiltinFSMonitor::
-	If set to true, enable the built-in file system monitor
+	(EXPERIMENTAL) If set to true, enable the built-in file system monitor
 	daemon for this working directory (linkgit:git-fsmonitor--daemon[1]).
 +
 Like hook-based file system monitors, the built-in file system monitor

Documentation/git-fsmonitor--daemon.txt

@@ -3,7 +3,7 @@ git-fsmonitor--daemon(1)
 
 NAME
 ----
-git-fsmonitor--daemon - A Built-in File System Monitor
+git-fsmonitor--daemon - (EXPERIMENTAL) A Built-in File System Monitor
 
 SYNOPSIS
 --------
@@ -16,6 +16,9 @@ SYNOPSIS
 DESCRIPTION
 -----------
 
+NOTE! This command is still only an experiment, subject to change dramatically
+(or even to be abandoned).
+
 A daemon to watch the working directory for file and directory
 changes using platform-specific file system notification facilities.