Update top-level docs to give a basic idea of status

Author: jeromekelleher

docs/intro.md

@@ -1,9 +1,25 @@
 # bio2zarr
 
 `bio2zarr` efficiently converts common bioinformatics formats to
-[Zarr](https://zarr.readthedocs.io/en/stable/) format. Initially supporting converting
-VCF to the [VCF Zarr specification](https://github.com/sgkit-dev/vcf-zarr-spec/).
+[Zarr](https://zarr.readthedocs.io/en/stable/) format.
+
+## Tools
+
+- {ref}`sec-vcf2zarr` converts VCF data to
+  [VCF Zarr](https://github.com/sgkit-dev/vcf-zarr-spec/) format.
+
+- {ref}`sec-vcfpartition` is a utility to split an input (set of)
+  VCFs into a given number of partitions. This is useful for
+  parallel processing.
+
+## Development status
 
 `bio2zarr` is in development, contributions, feedback and issues are welcome
 at the [GitHub repository](https://github.com/sgkit-dev/bio2zarr).
 
+Support for converting PLINK data to VCF Zarr is partially implemented,
+and adding BGEN support is also planned. If you would like to see
+support for other formats (or an interested in helping with implementing),
+please open an [issue on Github](https://github.com/sgkit-dev/bio2zarr/issues)
+to discuss!
+

docs/vcf2zarr/overview.md

@@ -1,7 +1,10 @@
+(sec-vcf2zarr)=
 # vcf2zarr
 
 
-Convert a VCF to zarr format:
+Convert VCF data to the
+[VCF Zarr specification](https://github.com/sgkit-dev/vcf-zarr-spec/)
+reliably, in parallel.
 
 ```
 $ vcf2zarr convert <VCF1> <VCF2> <zarr>

docs/vcfpartition/overview.md

@@ -1,3 +1,4 @@
+(sec-vcfpartition)=
 # vcfpartition
 
 ## Overview