format nnictl tutorial (#2599)

docs/en_US/Tutorial/Nnictl.md

@@ -28,7 +28,7 @@ nnictl support commands:
 ### Manage an experiment
 
 <a name="create"></a>
-![](https://placehold.it/15/1589F0/000000?text=+) `nnictl create`
+### nnictl create
 
 * Description
 
@@ -79,7 +79,7 @@ Debug mode will disable version check function in Trialkeeper.
 
 <a name="resume"></a>
 
-![](https://placehold.it/15/1589F0/000000?text=+) `nnictl resume`
+### nnictl resume
 
 * Description
 
@@ -110,7 +110,7 @@ Debug mode will disable version check function in Trialkeeper.
 
 <a name="view"></a>
 
-![](https://placehold.it/15/1589F0/000000?text=+) `nnictl view`
+### nnictl view
 
 * Description
 
@@ -138,7 +138,7 @@ Debug mode will disable version check function in Trialkeeper.
   ```
 
 <a name="stop"></a>
-![](https://placehold.it/15/1589F0/000000?text=+) `nnictl stop`
+### nnictl stop
 
 * Description
 
@@ -190,7 +190,7 @@ Debug mode will disable version check function in Trialkeeper.
 
 <a name="update"></a>
 
-![](https://placehold.it/15/1589F0/000000?text=+) `nnictl update`
+### nnictl update
 
 * __nnictl update searchspace__
   * Description
@@ -299,7 +299,7 @@ Debug mode will disable version check function in Trialkeeper.
     ```
 
 <a name="trial"></a>
-![](https://placehold.it/15/1589F0/000000?text=+) `nnictl trial`
+### nnictl trial
 
 * __nnictl trial ls__
 
@@ -348,7 +348,7 @@ Debug mode will disable version check function in Trialkeeper.
 
 <a name="top"></a>
 
-![](https://placehold.it/15/1589F0/000000?text=+) `nnictl top`
+### nnictl top
 
 * Description
 
@@ -368,7 +368,7 @@ Debug mode will disable version check function in Trialkeeper.
   |--time, -t|  False| |The interval to update the experiment status, the unit of time is second, and the default value is 3 second.|
 
 <a name="experiment"></a>
-![](https://placehold.it/15/1589F0/000000?text=+) `Manage experiment information`
+### Manage experiment information
 
 * __nnictl experiment show__
 
@@ -532,7 +532,7 @@ Debug mode will disable version check function in Trialkeeper.
     ```
 
 <a name="platform"></a>
-![](https://placehold.it/15/1589F0/000000?text=+) `Manage platform information`
+### Manage platform information
 
 * __nnictl platform clean__
 
@@ -558,7 +558,7 @@ Debug mode will disable version check function in Trialkeeper.
 
 
 <a name="config"></a>
-![](https://placehold.it/15/1589F0/000000?text=+) `nnictl config show`
+### nnictl config show
 
 * Description
 
@@ -572,7 +572,7 @@ Debug mode will disable version check function in Trialkeeper.
 
 <a name="log"></a>
 
-![](https://placehold.it/15/1589F0/000000?text=+) `Manage log`
+### Manage log
 
 * __nnictl log stdout__
 
@@ -643,12 +643,12 @@ Debug mode will disable version check function in Trialkeeper.
   |--trial_id, -T|  False| |ID of the trial to be found the log path, required when id is not empty.|
 
 <a name="webui"></a>
-![](https://placehold.it/15/1589F0/000000?text=+) `Manage webui`
+### Manage webui
 
 * __nnictl webui url__
 
 <a name="tensorboard"></a>
-![](https://placehold.it/15/1589F0/000000?text=+) `Manage tensorboard`
+### Manage tensorboard
 
 * __nnictl tensorboard start__
 
@@ -697,7 +697,7 @@ Debug mode will disable version check function in Trialkeeper.
 
 <a name="package"></a>
 
-![](https://placehold.it/15/1589F0/000000?text=+) `Manage package`
+### Manage package
 
 * __nnictl package install__
   * Description
@@ -806,7 +806,7 @@ Debug mode will disable version check function in Trialkeeper.
 
 <a name="ss_gen"></a>
 
-![](https://placehold.it/15/1589F0/000000?text=+) `Generate search space`
+### Generate search space
 
 * __nnictl ss_gen__
   * Description
@@ -837,7 +837,7 @@ Debug mode will disable version check function in Trialkeeper.
 
 <a name="version"></a>
 
-![](https://placehold.it/15/1589F0/000000?text=+) `Check NNI version`
+### Check NNI version
 
 * __nnictl --version__