Add documentation for existing TLS settings in consul input (#3931)

plugins/inputs/consul/README.md

-# Telegraf Input Plugin: Consul
+# Consul Input Plugin
 
-This plugin will collect statistics about all health checks registered in the Consul. It uses [Consul API](https://www.consul.io/docs/agent/http/health.html#health_state)
-to query the data. It will not report the [telemetry](https://www.consul.io/docs/agent/telemetry.html) but Consul can report those stats already using StatsD protocol if needed.
+This plugin will collect statistics about all health checks registered in the
+Consul. It uses [Consul API](https://www.consul.io/docs/agent/http/health.html#health_state)
+to query the data. It will not report the
+[telemetry](https://www.consul.io/docs/agent/telemetry.html) but Consul can
+report those stats already using StatsD protocol if needed.
 
-## Configuration:
+### Configuration:
 
-```
+```toml
 # Gather health check statuses from services registered in Consul
 [[inputs.consul]]
-  ## Most of these values defaults to the one configured on a Consul's agent level.
-  ## Optional Consul server address (default: "")
-  # address = ""
-  ## Optional URI scheme for the Consul server (default: "")
-  # scheme = ""
-  ## Optional ACL token used in every request (default: "")
+  ## Consul server address
+  # address = "localhost"
+
+  ## URI scheme for the Consul server, one of "http", "https"
+  # scheme = "http"
+
+  ## ACL token used in every request
   # token = ""
-  ## Optional username used for request HTTP Basic Authentication (default: "")
+
+  ## HTTP Basic Authentication username and password.
   # username = ""
-  ## Optional password used for HTTP Basic Authentication (default: "")
   # password = ""
-  ## Optional data centre to query the health checks from (default: "")
-  # datacentre = ""
-```
 
-## Measurements:
+  ## Data centre to query the health checks from
+  # datacentre = ""
 
-### Consul:
-Tags:
-- node: on which node check/service is registered on
-- service_name: name of the service (this is the service name not the service ID)
-- check_id
+  ## SSL Config
+  # ssl_ca = "/etc/telegraf/ca.pem"
+  # ssl_cert = "/etc/telegraf/cert.pem"
+  # ssl_key = "/etc/telegraf/key.pem"
+  ## If false, skip chain & host verification
+  # insecure_skip_verify = true
+```
 
-Fields:
-- check_name
-- service_id
-- status
-- passing
-- critical
-- warning
+### Metrics:
+
+- consul_health_checks
+  - tags:
+  	- node (node that check/service is registred on)
+  	- service_name
+  	- check_id
+  - fields:
+    - check_name
+    - service_id
+    - status
+    - passing (integer)
+    - critical (integer)
+    - warning (integer)
 
 `passing`, `critical`, and `warning` are integer representations of the health
 check state. A value of `1` represents that the status was the state of the
@@ -46,8 +57,6 @@ the health check at this sample.
 ## Example output
 
 ```
-$ telegraf --config ./telegraf.conf --input-filter consul --test
-* Plugin: consul, Collection 1
-> consul_health_checks,host=wolfpit,node=consul-server-node,check_id="serfHealth" check_name="Serf Health Status",service_id="",status="passing",passing=1i,critical=0i,warning=0i 1464698464486439902
-> consul_health_checks,host=wolfpit,node=consul-server-node,service_name=www.example.com,check_id="service:www-example-com.test01" check_name="Service 'www.example.com' check",service_id="www-example-com.test01",status="critical",passing=0i,critical=1i,warning=0i 1464698464486519036
+consul_health_checks,host=wolfpit,node=consul-server-node,check_id="serfHealth" check_name="Serf Health Status",service_id="",status="passing",passing=1i,critical=0i,warning=0i 1464698464486439902
+consul_health_checks,host=wolfpit,node=consul-server-node,service_name=www.example.com,check_id="service:www-example-com.test01" check_name="Service 'www.example.com' check",service_id="www-example-com.test01",status="critical",passing=0i,critical=1i,warning=0i 1464698464486519036
 ```

plugins/inputs/consul/consul.go

@@ -31,19 +31,28 @@ type Consul struct {
 }
 
 var sampleConfig = `
-  ## Most of these values defaults to the one configured on a Consul's agent level.
-  ## Optional Consul server address (default: "localhost")
+  ## Consul server address
   # address = "localhost"
-  ## Optional URI scheme for the Consul server (default: "http")
+
+  ## URI scheme for the Consul server, one of "http", "https"
   # scheme = "http"
-  ## Optional ACL token used in every request (default: "")
+
+  ## ACL token used in every request
   # token = ""
-  ## Optional username used for request HTTP Basic Authentication (default: "")
+
+  ## HTTP Basic Authentication username and password.
   # username = ""
-  ## Optional password used for HTTP Basic Authentication (default: "")
   # password = ""
-  ## Optional data centre to query the health checks from (default: "")
+
+  ## Data centre to query the health checks from
   # datacentre = ""
+
+  ## SSL Config
+  # ssl_ca = "/etc/telegraf/ca.pem"
+  # ssl_cert = "/etc/telegraf/cert.pem"
+  # ssl_key = "/etc/telegraf/key.pem"
+  ## If false, skip chain & host verification
+  # insecure_skip_verify = true
 `
 
 func (c *Consul) Description() string {