NOISSUE - Update Getting Started doc with CLI usage (#465)

* Update "getting started" docs with CLI usage

Signed-off-by: Ivan Milošević <iva@blokovi.com>

* Update CLI description

Signed-off-by: Ivan Milošević <iva@blokovi.com>

* Update CLI docs with help flag

Signed-off-by: Ivan Milošević <iva@blokovi.com>

docs/getting-started.md

@@ -328,6 +328,168 @@ mosquitto_sub -u <thing_id> -P <thing_key> -t channels/<channel_id>/messages -h
 If you are using TLS to secure MQTT connection, add `--cafile docker/ssl/certs/ca.crt`
 to every command.
 
+## CLI
+
+Mainflux CLI is another way to manage users, things, channels and messages.
+
+CLI can be downloaded as separate asset from [project realeses](https://github.com/mainflux/mainflux/releases) or it can be built with:
+
+```
+make cli
+```
+
+which will build `mainflux-cli` in `<project_root>/build` folder.
+
+Executing `build/mainflux-cli` without any arguments will output help with all available commands and flags:
+
+```
+Usage:
+  mainflux-cli [command]
+
+Available Commands:
+  channels    Manipulation with channels
+  help        Help about any command
+  msg         Send or retrieve messages
+  things      things <options>
+  users       users create/token <email> <password>
+  version     Get version of Mainflux Things Service
+
+Flags:
+  -c, --content-type string    Mainflux message content type (default "application/senml+json")
+  -h, --help                   help for mainflux-cli
+  -a, --http-prefix string     Mainflux http adapter prefix (default "http")
+  -i, --insecure               Do not check for TLS cert
+  -l, --limit uint             limit query parameter (default 100)
+  -m, --mainflux-url string    Mainflux host URL (default "http://localhost")
+  -o, --offset uint            offset query parameter
+  -t, --things-prefix string   Mainflux things service prefix
+  -u, --users-prefix string    Mainflux users service prefix
+
+Use "mainflux-cli [command] --help" for more information about a command.
+```
+
+You can execute each command with `-h` flag for more information about that command, e.g.
+
+```
+./mainflux-cli channels -h
+```
+
+will get you usage info:
+
+```
+Manipulation with channels: create, delete or update channels
+
+Usage:
+  mainflux-cli channels [flags]
+  mainflux-cli channels [command]
+
+Available Commands:
+  create      create <JSON_channel> <user_auth_token>
+  delete      delete <channel_id> <user_auth_token>
+  get         get all/<channel_id> <user_auth_token>
+  update      update <JSON_string> <user_auth_token>
+
+```
+
+### Service
+#### Get the service verison
+
+```
+./mainflux-cli version
+```
+
+### User management
+#### Create User
+
+```
+./mainflux-cli users create john.doe@email.com password
+```
+
+#### Login User
+
+```
+./mainflux-cli users token john.doe@email.com password
+```
+
+### System Provisioning
+#### Provision Device
+
+```
+./mainflux-cli things create '{"type":"device", "name":"nyDevice"}' <user_auth_token>
+```
+
+#### Provision Application
+
+```
+./mainflux-cli things create '{"type":"app", "name":"nyDevice"}' <user_auth_token>
+```
+
+#### Retrieve All Things
+
+```
+./mainflux-cli things get all --offset=1 --limit=5 <user_auth_token>
+```
+
+#### Retrieve Thing By ID
+
+```
+./mainflux-cli things get <thing_id> --offset=1 --limit=5 <user_auth_token>
+```
+
+#### Remove Thing
+
+```
+./mainflux-cli things delete <thing_id> <user_auth_token>
+```
+
+#### Provision Channel
+
+```
+./mainflux-cli channels create '{"name":"nyChannel"}' <user_auth_token>
+```
+
+#### Retrieve All Channels
+
+```
+./mainflux-cli channels get all --offset=1 --limit=5 <user_auth_token>
+```
+
+#### Retrievie Channel By ID
+
+```
+./mainflux-cli channels get <channel_id> --offset=1 --limit=5 <user_auth_token>
+```
+
+#### Remove Channel
+
+```
+./mainflux-cli channels delete <channel_id> <user_auth_token>
+```
+
+### Access control
+#### Connect Thing to a Channel
+
+```
+./mainflux-cli things connect <thing_id> <channel_id> <user_auth_token>
+```
+
+#### Disconnect Things from a Channel
+
+```
+./mainflux-cli things disconnect <thing_id> <channel_id> <user_auth_token>
+```
+
+### Messaging
+#### Send a message over HTTP
+
+```
+./mainflux-cli msg send <channel_id> '[{"bn":"some-base-name:","bt":1.276020076001e+09, "bu":"A","bver":5, "n":"voltage","u":"V","v":120.1}, {"n":"current","t":-5,"v":1.2}, {"n":"current","t":-4,"v":1.3}]' <thing_auth_token>
+```
+
+
+
+
+
 ## Add-ons
 
 The `<project_root>/docker` folder contains an `addons` directory. This directory is used for various services that are not core to the Mainflux platform but could be used for providing additional features.