Must include class/method documentation for CRAN check

* checking for missing documentation entries ... WARNING
Undocumented code objects:
  ‘add_months’ ‘agg’ ‘approxCountDistinct’ ‘approxQuantile’ ‘arrange’
  ‘array_contains’ ‘as.DataFrame’ ‘as.data.frame’ ‘asc’ ‘ascii’ ‘avg’
  ‘base64’ ‘between’ ‘bin’ ‘bitwiseNOT’ ‘bround’ ‘cache’ ‘cacheTable’
  ‘cancelJobGroup’ ‘cast’ ‘cbrt’ ‘ceil’ ‘clearCache’ ‘clearJobGroup’
  ‘collect’ ‘colnames’ ‘colnames<-’ ‘coltypes’ ‘coltypes<-’ ‘column’
  ‘columns’ ‘concat’ ‘concat_ws’ ‘contains’ ‘conv’ ‘corr’ ‘count’
  ‘countDistinct’ ‘cov’ ‘covar_pop’ ‘covar_samp’ ‘crc32’
  ‘createDataFrame’ ‘createExternalTable’ ‘createOrReplaceTempView’
  ‘crossJoin’ ‘crosstab’ ‘cume_dist’ ‘dapply’ ‘dapplyCollect’
  ‘date_add’ ‘date_format’ ‘date_sub’ ‘datediff’ ‘dayofmonth’
  ‘dayofyear’ ‘decode’ ‘dense_rank’ ‘desc’ ‘describe’ ‘distinct’ ‘drop’
...