Add an `rpc-tests` make target

This ensures that zcashd is up-to-date with any changes before running the
tests.

Makefile.am

@@ -13,7 +13,7 @@ SUBDIRS = src
 if ENABLE_MAN
 SUBDIRS += doc/man
 endif
-.PHONY: deploy FORCE
+.PHONY: deploy FORCE rpc-tests
 
 GZIP_ENV="-9n"
 
@@ -174,3 +174,6 @@ clean-local:
 distclean-local:
 	rm -f zcutil/bin/db_*
 	rmdir zcutil/bin 2>/dev/null || true
+
+rpc-tests: $(BITCOIND_BIN)
+	qa/pull-tester/rpc-tests.py $(RPC_TEST)

qa/README.md

@@ -27,19 +27,22 @@ Running tests
 
 You can run any single test by calling
 
-    qa/pull-tester/rpc-tests.py <testname>
+    RPC_TEST=<testname> make rpc-tests
 
 Or you can run any combination of tests by calling
 
-    qa/pull-tester/rpc-tests.py <testname1> <testname2> <testname3> ...
+    RPC_TEST="<testname1> <testname2> <testname3> ..." make rpc-tests
 
 Run the regression test suite with
 
-    qa/pull-tester/rpc-tests.py
+    make rpc-tests
 
 Run all possible tests with
 
-    qa/pull-tester/rpc-tests.py --extended
+    RPC_TEST="--extended" make rpc-tests
+
+You can also run the tests directly using `qa/pull-tester/rpc-tests.py` instead
+of `make`, but that won't ensure that zcashd is up-to-date with any changes.
 
 By default, tests will be run in parallel. To specify how many jobs to run,
 append `--jobs=n` (default n=4).