Add docs information on renaming

Author: apeltzer

docs/usage.md

@@ -168,7 +168,7 @@ If you prefer, you can specify the full path to your reference genome when you r
 ```bash
 --fasta '[path to Fasta reference]'
 ```
-> If you don't specify appropriate `--bwa_index`, `--fasta_index` parameters, the pipeline will create these indices for you automatically. Note, that saving these for later has to be turned on using `--saveReference`. You may also specify the path to a gzipped (`*.gz` file extension) FastA as reference genome - this will be uncompressed by the pipeline automatically for you.
+> If you don't specify appropriate `--bwa_index`, `--fasta_index` parameters, the pipeline will create these indices for you automatically. Note, that saving these for later has to be turned on using `--saveReference`. You may also specify the path to a gzipped (`*.gz` file extension) FastA as reference genome - this will be uncompressed by the pipeline automatically for you. Note that other file extensions such as `.fna`, `.fa` are also supported but will be renamed to `.fasta` automatically by the pipeline.
 
 ### `--genome` (using iGenomes)