Add package slack to the index

index/slack.mk

@@ -0,0 +1,7 @@
+PACKAGES += slack
+pkg_slack_name = slack
+pkg_slack_description = Minimal slack notification OTP library.
+pkg_slack_homepage = https://github.com/DonBranson/slack
+pkg_slack_fetch = git
+pkg_slack_repo = https://github.com/DonBranson/slack.git
+pkg_slack_commit = 1.0.0