Update device-tree.md

3, 38, 109, 152, 169, 174, 176, 178, 202, 218, 238,448, 471, 474, 612, 627, 781, 822
line 560: added backticks to /proc/device-tree
line 627: added backticks to dtoverlay-pre and -post
line 633: added backticks to /clocks
line 683: added backticks to /proc/device-tree
line 687: added backticks to config.txt
line 689: added backticks to dtmerge
line 822: added backticks to enable_uart=1
3.5.3, third item: This can lead to kernel exceptions when an overlay is unloaded if a codec is deleted before the card using it.

Author: JaninaPi