README: Add a section describing MicroPython's values. #28

Job	Run time
build_idf (esp32_build_cmod_spiram_s2)	4m 19s
build_idf (esp32_build_s3_c3)	3m 13s
build_idf (esp32_build_c2_c5_c6)	3m 51s
build_idf (esp32_build_p4)	3m 10s
	14m 33s

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