readme: add build info

readme.md

@@ -23,6 +23,7 @@ api:
   insecure: false
 # https://golang.org/src/time/format.go#L57
 date_format: 02/01/2006 15:04:05 MST
+slack_webhook: https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX
 monitors:
   # http monitor example
   - name: google
@@ -172,3 +173,12 @@ We'll happily accept contributions for the following (non exhaustive list).
 - Implement TCP check
 - Any bug fixes / code improvements
 - Test cases
+
+# Build on MacOS
+1. Read and install with https://ahmadawais.com/install-go-lang-on-macos-with-homebrew/
+
+2. Test in console with `go get -u` and `go build cli/main.go`
+
+3. Run `./go-executable-build.sh cli/main.go`
+
+4. `mv cli/main.go-linux-amd64 cachet-monitor-linux-amd64`