Add install and build instructions, refactor docs structure #1110

Job	Run time
cpp-beam_search_causal_lm-Qwen-7B-Chat	10m 7s
cpp-beam_search_causal_lm-ubuntu (./build/samples/cpp/beam_search_causal_lm/beam_search_causal_lm)	10m 7s
cpp-beam_search_causal_lm-ubuntu (python ./samples/python/beam_search_causal_lm/beam_search_causa...	10m 41s
cpp-greedy_causal_lm-windows	0s
cpp-multinomial-greedy_causal_lm-ubuntu	7m 56s
cpp-beam_search_causal_lm-notus-7b-v1	7m 36s
cpp-beam_search_causal_lm-Phi-2	5m 54s
cpp-beam_search_causal_lm-Qwen1_5-7B-Chat	9m 13s
cpp-greedy_causal_lm-redpajama-3b-chat	13m 29s
cpp-Phi-1_5	6m 49s
cpp-prompt_lookup_decoding_lm-ubuntu	7m 30s
cpp-speculative_decoding_lm-ubuntu	11m 27s
	1h 40m 49s

Provide feedback