Merge #652: README.md: update instruction to run tests

ce6d438 README.md: update instruction to run tests (Marko Bencun)

Pull request description:

  Reflecting what Travis does.

ACKs for commit ce6d43:
  real-or-random:
    ACK ce6d438
  sipa:
    ACK ce6d438

Tree-SHA512: c0a36772a5d8571bb503f83111e89181acc1eec080cf7efa64ab922f6136138234555a9d47120e2126ae958a60864b0479c3037bff74895dd488015f25a05c10

README.md

@@ -59,5 +59,5 @@ libsecp256k1 is built using autotools:
     $ ./autogen.sh
     $ ./configure
     $ make
-    $ ./tests
+    $ make check
     $ sudo make install  # optional