Merge #1483: cmake: Recommend native CMake commands in README

3777e3f cmake: Recommend native CMake commands in README (Tim Ruffing)

Pull request description:

ACKs for top commit:
  hebasto:
    ACK 3777e3f
  jonasnick:
    ACK 3777e3f

Tree-SHA512: 884e54ee3ec9617edbb98d439ccd3fa8b3d9448969a4f5a88d22d034329ec5024238d6f91e28160f82f77eed678100266ac8b5495b6072b48caa0514a9cec881

README.md

@@ -79,9 +79,9 @@ To maintain a pristine source tree, CMake encourages to perform an out-of-source
 
     $ mkdir build && cd build
     $ cmake ..
-    $ make
-    $ make check  # run the test suite
-    $ sudo make install  # optional
+    $ cmake --build .
+    $ ctest  # run the test suite
+    $ sudo cmake --build . --target install  # optional
 
 To compile optional modules (such as Schnorr signatures), you need to run `cmake` with additional flags (such as `-DSECP256K1_ENABLE_MODULE_SCHNORRSIG=ON`). Run `cmake .. -LH` to see the full list of available flags.