Added build instructions

docs/backend/README.md

@@ -82,3 +82,11 @@ option = 'Fifth square'
 Having the same header `[[]]` puts them in a list
 
 Both the config and a single dataset is required
+
+## Building
+- Install rust
+- clone repo
+- `cd repodir/backend`
+- `cargo build`
+
+Done