doc: board: sdm845: Explicitly add boot.img flashing command

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>

Use code-block. Fix length of two heading underlines.
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/board/qualcomm/sdm845.rst b/doc/board/qualcomm/sdm845.rst
index 71879c2..d3f218e 100644
--- a/doc/board/qualcomm/sdm845.rst
+++ b/doc/board/qualcomm/sdm845.rst
@@ -38,9 +38,10 @@
 with appended dtb, so let's mimic linux to satisfy stock bootloader.
 
 Boards
-------------
+------
+
 starqlte
-^^^^^^^^^^^^
+^^^^^^^^
 
 The starqltechn is a production board for Samsung S9 (SM-G9600) phone,
 based on the Qualcomm SDM845 SoC.
@@ -149,7 +150,11 @@
 	mkbootimg --kernel u-boot.bin.gz-dtb --ramdisk db845c.itb \
 	--output boot.img --pagesize 4096 --base 0x80000000
 
-- Flash boot.img using db845c fastboot method.
+- Flash boot.img using db845c fastboot method:
+
+  .. code-block:: bash
+
+      sudo fastboot flash boot boot.img
 
 More information can be found on the `DragonBoard 845c page`_.