Mention how to copy & paste in fenced code blocks more clearly #1910

Job	Run time
cppcheck	17m 40s
code formatting check	14s
min features with gcc	2m 3s
min features with g++	2m 44s
min features with clang	2m 15s
max features with gcc	3m 13s
max features with g++	2m 52s
max features with clang	3m 21s
max features with gcc and DEBUG	2m 35s
max features with gcc for 32-bit arch (legacy OS)	1m 38s
max features with g++ for 32-bit arch (legacy OS)	1m 20s
max features with clang for 32-bit arch (legacy OS)	1m 42s
	41m 37s

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