Generate cache and save it on first run

src/pgd.rs

@@ -18,7 +18,11 @@ fn main_with_cache(request: &str, regen: bool) -> Result<()> {
 
     let (cache, just_generated) = match Cache::read() {
         Ok(c) => (c, false),
-        Err(_) => (Cache::generate(), true),
+        Err(_) => {
+            let cache = Cache::generate();
+            cache.write()?;
+            (cache, true)
+        },
     };
 
     let only_match = match cache.find_interactive(&request) {