feat: add landing page and basic index for chart-releaser

_config.yml

+theme: jekyll-theme-cayman
+name: InfluxData Helm Charts
+description: InfluxData Helm Charts for InfluxDB, Telegraf, and others

index.md

+# InfluxData Helm Repository
+
+![InfluxData](https://influxdata.github.io/branding/img/downloads/influxdata-logo--tagline--castle-alpha.png)
+
+## Add the InfluxData Helm repository
+
+```bash
+helm repo add influxdata https://influxdata.github.io/helm-charts
+```
+
+## Install InfluxDB
+
+```bash
+helm upgrade -i influxdb influxdata/influxdb
+```
+
+For more details on installing InfluxDB please see the [chart's README](https://github.com/influxdata/helm-charts/tree/master/charts/influxdb).

index.yaml

+apiVersion: v1