Input Output column md file for regression and ranking. (#3447)

* Input Output column md file for regression and ranking.:

* changes.

* changes.

* revert.

Author: codemzs

docs/api-reference/io-columns-binary-classification.md

@@ -1,5 +1,5 @@
 ### Input and Output Columns
-The input label column data must be <xref:System.Single>. This trainer outputs the following columns:
+The input label column data must be <xref:System.Boolean>. This trainer outputs the following columns:
 
 | Output Column Name | Column Type | Description|
 | -- | -- | -- |

docs/api-reference/io-columns-ranking.md

@@ -0,0 +1,7 @@
+### Input and Output Columns
+The input label column data must be <xref:System.Single> and input group column
+data must be <xref:System.UInt32>. This trainer outputs the following columns:
+
+| Output Column Name | Column Type | Description|
+| -- | -- | -- |
+| `Score` | <xref:System.Single> | The unbounded score that was calculated by the model to determine the prediction.|

docs/api-reference/io-columns-regression.md

@@ -0,0 +1,6 @@
+### Input and Output Columns
+The input label column data must be <xref:System.Single>. This trainer outputs the following columns:
+
+| Output Column Name | Column Type | Description|
+| -- | -- | -- |
+| `Score` | <xref:System.Single> | The unbounded score that was predicted by the model.|