Error(s) in re-building vignettes:
  ...
--- re-building 'introduction.Rmd' using rmarkdown
Installing package into '/home/hornik/tmp/R.check/r-devel-clang/Work/build/Packages'
(as 'lib' is unspecified)
Warning in install.packages("SleepCycles", repos = "http://cran.us.r-project.org") :
  'lib = "/home/hornik/tmp/R.check/r-devel-clang/Work/build/Packages"' is not writable
Quitting from lines 51-56 (introduction.Rmd) 
Error: processing vignette 'introduction.Rmd' failed with diagnostics:
unable to install packages
--- failed re-building 'introduction.Rmd'

SUMMARY: processing the following file failed:
  'introduction.Rmd'

Error: Vignette re-building failed.
Execution halted
Error(s) in re-building vignettes:
  ...
--- re-building ‘introduction.Rmd’ using rmarkdown
Installing package into '/home/hornik/tmp/R.check/r-devel-gcc/Work/build/Packages'
(as 'lib' is unspecified)
Warning in install.packages("SleepCycles", repos = "http://cran.us.r-project.org") :
  'lib = "/home/hornik/tmp/R.check/r-devel-gcc/Work/build/Packages"' is not writable
Quitting from lines 51-56 (introduction.Rmd) 
Error: processing vignette 'introduction.Rmd' failed with diagnostics:
unable to install packages
--- failed re-building ‘introduction.Rmd’

SUMMARY: processing the following file failed:
  ‘introduction.Rmd’

Error: Vignette re-building failed.
Execution halted