Added build instructions

docs/backend/README.md

@@ -81,4 +81,12 @@ option = 'Fifth square'
 
 Having the same header `[[]]` puts them in a list
 
-Both the config and a single dataset is required
+Both the config and a single dataset is required
+
+## Building
+- Install rust
+- clone repo
+- `cd repodir/backend`
+- `cargo build`
+
+Done