Basic documentation for shell completion

Closes #87

Author: jeromekelleher

README.md

@@ -31,6 +31,7 @@ and will always work.
 
 ## vcf2zarr
 
+
 Convert a VCF to zarr format:
 
 ```
@@ -72,6 +73,21 @@ vcf2zarr encode tmp/sample.exploded tmp/sample.zarr -s sample.schema.json
 Use the ``-p, --worker-processes`` argument to control the number of workers used
 in the ``explode`` and ``encode`` phases.
 
+### Shell completion
+
+To enable shell completion for a particular session in Bash do:
+
+```
+eval "$(_VCF2ZARR_COMPLETE=bash_source vcf2zarr)" 
+```
+
+If you add this to your ``.bashrc`` vcf2zarr shell completion should available
+in all new shell sessions.
+
+See the [Click documentation](https://click.palletsprojects.com/en/8.1.x/shell-completion/#enabling-completion)
+for instructions on how to enable completion in other shells.
+a
+
 ## plink2zarr
 
 Convert a plink ``.bed`` file to zarr format. **This is incomplete**