btrfs-progs: docs: separate bootloaders chapter

Used in manual page section 5 and Administration overview.

Signed-off-by: David Sterba <dsterba@suse.com>

Documentation/Administration.rst

@@ -8,3 +8,8 @@ Mount options
 -------------
 
 .. include:: ch-mount-options.rst
+
+Bootloaders
+-----------
+
+.. include:: ch-bootloaders.rst

Documentation/btrfs-man5.rst

@@ -254,18 +254,7 @@ minimum filesystem size
 BOOTLOADER SUPPORT
 ------------------
 
-GRUB2 (https://www.gnu.org/software/grub) has the most advanced support of
-booting from BTRFS with respect to features.
-
-U-boot (https://www.denx.de/wiki/U-Boot/) has decent support for booting but
-not all BTRFS features are implemented, check the documentation.
-
-EXTLINUX (from the https://syslinux.org project) can boot but does not support
-all features. Please check the upstream documentation before you use it.
-
-The first 1MiB on each device is unused with the exception of primary
-superblock that is on the offset 64KiB and spans 4KiB.
-
+.. include:: ch-bootloaders.rst
 
 FILE ATTRIBUTES
 ---------------

Documentation/ch-bootloaders.rst

@@ -0,0 +1,11 @@
+GRUB2 (https://www.gnu.org/software/grub) has the most advanced support of
+booting from BTRFS with respect to features.
+
+U-boot (https://www.denx.de/wiki/U-Boot/) has decent support for booting but
+not all BTRFS features are implemented, check the documentation.
+
+EXTLINUX (from the https://syslinux.org project) can boot but does not support
+all features. Please check the upstream documentation before you use it.
+
+The first 1MiB on each device is unused with the exception of primary
+superblock that is on the offset 64KiB and spans 4KiB.