Adding workaround for install the R-package

I was facing this issue and this workaround worked for me. Maybe this should be moved to know issues section.

R-package/README.md

@@ -1,6 +1,8 @@
-# R package for xgboost.
+R package for xgboost
+=====================
 
-## Installation
+Installation
+------------
 
 For up-to-date version (which is recommended), please install from github. Windows user will need to install [RTools](http://cran.r-project.org/bin/windows/Rtools/) first.
 
@@ -8,8 +10,26 @@ For up-to-date version (which is recommended), please install from github. Windo
 devtools::install_github('dmlc/xgboost',subdir='R-package')
 ```
 
-
-## Examples
+Examples
+--------
 
 * Please visit [walk through example](demo).
 * See also the [example scripts](../demo/kaggle-higgs) for Kaggle Higgs Challenge, including [speedtest script](../demo/kaggle-higgs/speedtest.R) on this dataset and the one related to [Otto challenge](../demo/kaggle-otto), including a [RMarkdown documentation](../demo/kaggle-otto/understandingXGBoostModel.Rmd).
+
+Notes
+-----
+
+If you face an issue installing the package using  ```devtools::install_github```, something like this (even after updating libxml and RCurl as lot of forums say) -
+
+```
+devtools::install_github('dmlc/xgboost',subdir='R-package')
+Downloading github repo dmlc/xgboost@master
+Error in function (type, msg, asError = TRUE)  : 
+  Peer certificate cannot be authenticated with given CA certificates
+```
+To get around this you can build the package locally as mentioned [here](https://github.com/dmlc/xgboost/issues/347) - 
+```
+1. Clone the current repository and set your workspace to xgboost/R-package/
+2. Run R CMD INSTALL --build . in terminal to get the tarball.
+3. Run install.packages('path_to_the_tarball',repo=NULL) in R to install.
+```