Add Makefile help comments

Commit [1] that originally introduced make help target also had special
comments (starting with ###) for help target to parse.
Makefile that was finally merged after some changes lacked this
comments. Without this comments when executed help prints empty output.

PR: #371
[1]: 72133e9

Signed-off-by: Wojciech Szarański <wojciech.szaranski@gmail.com>

Makefile

@@ -1,19 +1,19 @@
 .PHONY: test testrace int ci clean help
-test:
+test: ### Run unit tests
 	go test ./...
 
-testrace:
+testrace: ### Run unit tests with race detector
 	go test -race ./...
 
-int:
+int: ### Run integration tests (doesn't download redis server)
 	${MAKE} -C integration int
 
-ci:
+ci: ### Run full tests suite (including download and compilation of proper redis server)
 	${MAKE} test
 	${MAKE} -C integration redis_src/redis-server int
 	${MAKE} testrace
 
-clean:
+clean: ### Clean integration test files and remove compiled redis from integration/redis_src
 	${MAKE} -C integration clean
 
 help: