Mention pynvim requirement (#356) #37

Job	Run time
Coq integration tests (8.4, 3.6)	41s
Coq integration tests (8.5, 3.6)	53s
Coq integration tests (8.6, 3.6)	51s
Coq integration tests (8.7, 3.6)	47s
Coq integration tests (8.8, 3.6)	51s
Coq integration tests (8.9, 3.6)	49s
Coq integration tests (8.10, 3.6)	1m 4s
Coq integration tests (8.11, 3.6)	53s
Coq integration tests (8.12, 3.6)	52s
Coq integration tests (8.13, 3.6)	57s
Coq integration tests (8.14, 3.6)	1m 9s
Coq integration tests (8.15, 3.6)	53s
Coq integration tests (8.16, 3.6)	57s
Coq integration tests (8.17, 3.6)	57s
Coq integration tests (8.18, 3.6)	59s
Coq integration tests (8.19, 3.6)	1m 7s
Coq integration tests (master, 3.6)	4m 1s
	18m 41s

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