Add the indoc crate to help clean up examples

[JoshuaBatty]

closes #638

[kayagokalp]

Should we also use it for:

fuelup/tests/default.rs

Lines 60 to 63 in 2d81994

	"Toolchain with name 'nightly-{}' does not exist\n\n\
	\u{1b}[1mInstalled toolchains\u{1b}[0m\n\
	--------------------\n\
	latest-{}\n\n",

to remove the need of explicitly using /n in the expected case or if you think these are fine, happy to approve.

[JoshuaBatty]

Should we also use it for:

fuelup/tests/default.rs

Lines 60 to 63 in 2d81994

	"Toolchain with name 'nightly-{}' does not exist\n\n\
	\u{1b}[1mInstalled toolchains\u{1b}[0m\n\
	--------------------\n\
	latest-{}\n\n",

to remove the need of explicitly using /n in the expected case or if you think these are fine, happy to approve.

Yeah good call, might as well add it here as well. Will push a commit now

[JoshuaBatty]

actually i'll leave it as is for now as these contain bold formatting in places.