Fix broken links. (#6455)

Co-authored-by: Hao Ziyu <haoziyu@qiyi.com>
Co-authored-by: fis <jm.yuan@outlook.com>

demo/CLI/binary_classification/README.md

@@ -62,7 +62,7 @@ test:data = "agaricus.txt.test"
 We use the tree booster and logistic regression objective in our setting. This indicates that we accomplish our task using classic gradient boosting regression tree(GBRT), which is a promising method for binary classification.
 
 The parameters shown in the example gives the most common ones that are needed to use xgboost.
-If you are interested in more parameter settings, the complete parameter settings and detailed descriptions are [here](../../doc/parameter.rst). Besides putting the parameters in the configuration file, we can set them by passing them as arguments as below:
+If you are interested in more parameter settings, the complete parameter settings and detailed descriptions are [here](https://xgboost.readthedocs.io/en/stable/parameter.html). Besides putting the parameters in the configuration file, we can set them by passing them as arguments as below:
 
 ```
 ../../xgboost mushroom.conf max_depth=6
@@ -161,4 +161,3 @@ Eg. ```nthread=10```
 
 Set nthread to be the number of your real cpu (On Unix, this can be found using ```lscpu```)
 Some systems will have ```Thread(s) per core = 2```, for example, a 4 core cpu with 8 threads, in such case set ```nthread=4``` and not 8.
-

demo/CLI/regression/README.md

@@ -1,6 +1,6 @@
 Regression
 ====
-Using XGBoost for regression is very similar to using it for binary classification. We suggest that you can refer to the [binary classification demo](../binary_classification) first. In XGBoost if we use negative log likelihood as the loss function for regression, the training procedure is same as training binary classifier of XGBoost. 
+Using XGBoost for regression is very similar to using it for binary classification. We suggest that you can refer to the [binary classification demo](../binary_classification) first. In XGBoost if we use negative log likelihood as the loss function for regression, the training procedure is same as training binary classifier of XGBoost.
 
 ### Tutorial
 The dataset we used is the [computer hardware dataset from UCI repository](https://archive.ics.uci.edu/ml/datasets/Computer+Hardware). The demo for regression is almost the same as the [binary classification demo](../binary_classification), except a little difference in general parameter:
@@ -14,4 +14,3 @@ objective = reg:squarederror
 ```
 
 The input format is same as binary classification, except that the label is now the target regression values. We use linear regression here, if we want use objective = reg:logistic logistic regression, the label needed to be pre-scaled into [0,1].
-

demo/README.md

@@ -60,9 +60,9 @@ This is a list of short codes introducing different functionalities of xgboost p
 Most of examples in this section are based on CLI or python version.
 However, the parameter settings can be applied to all versions
 
-- [Binary classification](binary_classification)
+- [Binary classification](CLI/binary_classification)
 - [Multiclass classification](multiclass_classification)
-- [Regression](regression)
+- [Regression](CLI/regression)
 - [Learning to Rank](rank)
 
 ### Benchmarks

doc/tutorials/model.rst

@@ -2,7 +2,6 @@
 Introduction to Boosted Trees
 #############################
 XGBoost stands for "Extreme Gradient Boosting", where the term "Gradient Boosting" originates from the paper *Greedy Function Approximation: A Gradient Boosting Machine*, by Friedman.
-This is a tutorial on gradient boosted trees, and most of the content is based on `these slides <http://homes.cs.washington.edu/~tqchen/pdf/BoostedTree.pdf>`_ by Tianqi Chen, the original author of XGBoost.
 
 The **gradient boosted trees** has been around for a while, and there are a lot of materials on the topic.
 This tutorial will explain boosted trees in a self-contained and principled way using the elements of supervised learning.