Mention that `gen_range` may overflow for floats #608

Job	Run time
test-cross (ubuntu-latest, powerpc-unknown-linux-gnu, stable)	1m 51s
Check doc	2m 15s
test-ios	26s
test (ubuntu-latest, x86_64-unknown-linux-gnu, stable)	1m 29s
test-miri	4m 52s
test (macos-latest, x86_64-apple-darwin, stable)	1m 17s
test-no-std	20s
test (windows-latest, x86_64-pc-windows-gnu, stable)	4m 16s
test (windows-latest, x86_64-pc-windows-msvc, beta)	3m 9s
test (ubuntu-latest, x86_64-unknown-linux-gnu, MSRV, 1.60.0)	7m 28s
test (ubuntu-latest, sudo apt-get update ; sudo apt install gcc-multilib, i686-unknown-linux-gnu,...	3m 23s
test (ubuntu-latest, x86_64-unknown-linux-gnu, nightly, minimal_versions)	2m 18s
	33m 4s

Provide feedback