Update README.md

README.md

@@ -111,7 +111,7 @@ tb.soft_masked_blocks("chr1")
 tb.masked? # true / false
 ```
 
-## hg19, hg38, hs1
+## hg19, hg38, hs1...
 
 Some reference genomes are provided as classes in advance. These classes automatically download 2bit files from the UCSC site into a cache directory upon first use.
 
@@ -121,6 +121,8 @@ hg38 = Bio::TwoBit::Hg38.new
 hs1  = Bio::TwoBit::Hs1.new
 ```
 
+Adding a new reference file is easy. Add [here](https://github.com/ruby-on-bioc/bio-twobit/blob/main/lib/bio/twobit/references/template.erb) the id of the genome you want to use. Pull requests are welcome.
+
 ## Development
 
 Bug reports and pull requests are welcome on GitHub at https://github.com/ruby-on-bioc/bio-twobit.