fix: repo_ref 'not found' err suggest `ngit init'

if the nostr remote was created by the maintainer before
`ngit init` was ran.

the error is more likely to occur when a user clones a repo using
the nostr remote whist the relay in the hint is down and the fallback
relays dont have the announcement. or if the user is offline when
they clone.

src/lib/client.rs

@@ -855,7 +855,7 @@ pub async fn get_repo_ref_from_cache(
     let repo_ref = RepoRef::try_from((
         repo_events
             .first()
-            .context("no repo announcement event found at specified coordinates")?
+            .context("no repo announcement event found at specified coordinates. if you are the repository maintainer consider running `ngit init` to create one")?
             .clone(),
         repo_coordinates
             .iter()