add app command docs #42

docs/appbase/app.md

+# app
+
+`app` command display detailed information about a single app.
+
+The most basic syntax to use it is -
+
+```sh
+abc app AppName
+```
+
+It can also take `AppID` in place of `AppName`.
+
+```sh
+abc app AppID
+```
+
+The above commands will only give basic details of the app such as its name, ID, ElasticSearch version etc.
+
+If you want more details such as credentials and metrics, you can pass in defined switches. The full version of `app` command looks like-
+
+```sh
+abc app [-c|--creds] [-m|--metrics] [ID|Appname]
+```
+
+#### Example
+
+```sh
+> abc app -cm MyCoolApp
+
+ID:         2000       
+Name:       MyCoolApp
+ES Version: 2.2.0
+
+Admin API key:      USER:PASS
+Read-only API key:  USER:PASS
+
+Storage:    4242
+Records:    42
++-------+-----------+---------+
+| DATE  | API CALLS | RECORDS |
++-------+-----------+---------+
+| 13-05 |     8     |    2    |
+| 14-05 |     10    |    2    |
+| ..... |     ..    |   ...   |
++-------+-----------+---------+
+| TOTAL |     18    |    4    |
++-------+-----------+---------+
+```
+
+⭐️ It shows API calls and number of records created on a per day basis (just like the graph you see on dashboard.appbase.io).