doc: extend docs of Graph.Watts_Strogatz(), closes #702 #1379

Job	Run time
Build wheels on Linux (aarch64/musllinux)	0s
Build wheels on Linux (aarch64/musllinux)	0s
Build wheels on Linux (x86_64)	21m 39s
Build wheels on Linux (x86_64)	21m 39s
Build wheels on Linux (i686)	21m 0s
Build wheels on Linux (i686)	21m 0s
Build sdist and test extra dependencies	3m 38s
Build sdist and test extra dependencies	3m 38s
Build wheels on Linux (aarch64/manylinux)	0s
Build wheels on Linux (aarch64/manylinux)	0s
Build wheels on macOS (x86_64)	12m 21s
Build wheels on macOS (x86_64)	31m 6s
Build wheels on macOS (arm64)	9m 57s
Build wheels on macOS (arm64)	9m 57s
Build wheels for WebAssembly	7m 54s
Build wheels for WebAssembly	7m 54s
Build wheels on Windows (Win32)	23m 26s
Build wheels on Windows (Win32)	23m 26s
Build wheels on Windows (x64)	41m 33s
Build wheels on Windows (x64)	41m 33s
Build with sanitizers for debugging purposes	10m 56s
Build with sanitizers for debugging purposes	10m 56s
	5h 23m 33s

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