install.packages("stm", repos='http://cran.us.r-project.org')
install.packages("igraph", repos='http://cran.us.r-project.org')
install.packages("wordcloud", repos='http://cran.us.r-project.org')
devtools::install_github("mroberts/stmBrowser",dependencies=TRUE)
install.packages("topicmodels", repos='http://cran.us.r-project.org')

If you have any problems to install the package «stmBrowser», please download it from 
http://www.luigicurini.com/uploads/6/7/9/8/67985527/stmbrowser_1.0.tar.gz 
and install it on R as «local files»