Added a basic README to point to the vignette.

README.md

@@ -0,0 +1,7 @@
+# Gene set searching in R
+
+![R CMD check](https://github.com/gesel-inc/gesel-R/actions/workflows/r-cmd-check.yaml/badge.svg)
+![Build pkgdown](https://github.com/gesel-inc/gesel-R/actions/workflows/build-pkgdown.yaml/badge.svg)
+
+Pretty much as it says on the tin - implements an R client to interact with the [Gesel database](https://github.com/LTLA/gesel-feedstock) for gene set searching.
+Check out the [user's guide](https://gesel-inc.github.io/gesel-R) for more details.