Add landing page to exporter

[ashleyprimo]

This is a PR per issue #69 to add a landing page to the exporter instead of a 404 error page 😃 (sorry for the failed previous PR)

[MalloZup]

thx

[MalloZup]

@ashleyprimo can we have a screenshot attached to see how it looks like?

optional: can you check why is travis failing? thx sofar!

[MalloZup]

#74

[ashleyprimo]

@MalloZup

@ashleyprimo can we have a screenshot attached to see how it looks like?

You can take a look at a preview image here, https://ashleyprimo.com/uploads/JEwPXOU3iJDAy1K0raaq.png - It's fairly simple however happy to make changes as needed. :)

In regards to the Travis CI failure, preliminary checks suggest that it's related to lack of gofmt -w . of my code; the diff after doing so is:

diff --git a/ha_cluster_exporter.go b/ha_cluster_exporter.go
index fce2e44..5e51291 100644
--- a/ha_cluster_exporter.go
+++ b/ha_cluster_exporter.go
@@ -114,4 +114,4 @@ func main() {
        http.Handle("/metrics", promhttp.Handler())
        log.Infoln("Serving metrics on port", *portNumber)
        log.Fatal(http.ListenAndServe(fmt.Sprintf(":%s", *portNumber), nil))
-}
\ No newline at end of file
+}
diff --git a/vendor/github.com/sirupsen/logrus/terminal_check_bsd.go b/vendor/github.com/sirupsen/logrus/terminal_check_bsd.go
index 3c4f43f..ff6ff7b 100644
--- a/vendor/github.com/sirupsen/logrus/terminal_check_bsd.go
+++ b/vendor/github.com/sirupsen/logrus/terminal_check_bsd.go
@@ -10,4 +10,3 @@ func isTerminal(fd int) bool {
        _, err := unix.IoctlGetTermios(fd, ioctlReadTermios)
        return err == nil
 }
-

[MalloZup]

@ashleyprimo nice thx!
LGTM we will merge this PR after we release the current master.

good work!