Some file and tool names in README are wrong

[mptrsen]

In the README under "Running the pipeline":

2.:

• build_splicegraph should be build_splice_graph
• genome_k25_m100M_l1.bloom should be genome_k25_m500M_l1.bf

3.:
Neither gfa_to_exons nor gfa_to_gapped_transcript exist. Instead, gfa1_to_fasta is there and seems to have options that modify its behaviour according to the other two tools. Amend the instructions to reflect this.