Add wasm build instructions and fdtd3dbench target with predefined co… #85

Job	Run time
Unit test x64 ubuntu 22.04 for parallel grid CXX11=ON	42m 45s
Unit test x64 ubuntu 22.04 for grid	2m 36s
Unit test x64 ubuntu 22.04 for clock	2m 55s
Unit test x64 ubuntu 22.04 for parallel grid CXX11=OFF	46m 59s
Unit test x64 ubuntu 22.04 for dumpers-loaders	5m 44s
Unit test x64 ubuntu 22.04 for coordinate	1m 56s
Unit test x64 ubuntu 22.04 for settings	1m 2s
Unit test x64 ubuntu 22.04 for layout	38m 4s
Unit test x64 ubuntu 22.04 for internalscheme	24m 5s
Unit test x64 ubuntu 22.04 for approximation	2m 48s
Unit test x64 ubuntu 22.04 for complex	35s
	2h 49m 29s

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