Grammar corrections followup to #510 (#512)

A very small commit, but let's do all the string corrections while I am already at it :-)

Wraps up #510

src/main.rs

@@ -98,8 +98,8 @@ Then try to restart Plume.
             SearcherError::IndexOpeningError => panic!(
                 r#"
 Plume was unable to open the search index. If you created the index
-before, make sure to run Plume in the directory it was created, or 
-to set SEARCH_INDEX accordingly. If you did not create the search 
+before, make sure to run Plume in the same directory it was created in, or 
+to set SEARCH_INDEX accordingly. If you did not yet create the search 
 index, run this command:
 
     plm search init