updated Readme removed seq bug in task1_2

Updated Readme to reflect the need to use the base directory, not the
actual data file

Fixed a bug in function “get_percentage_read_length” where function did
not actually assess the length of the sequence by not calling for
sequence.seq (a.seq)

Simplified counting expression in “get_percentage_read_length” to use
filter() instead of nesting reduce() and map() expressions to achieve
the same thing.