Fix missing doc errors

src/engines/duckduckgo.rs

@@ -18,7 +18,7 @@ use super::search_result_parser::SearchResultParser;
 /// A new DuckDuckGo engine type defined in-order to implement the `SearchEngine` trait which allows to
 /// reduce code duplication as well as allows to create vector of different search engines easily.
 pub struct DuckDuckGo {
-    // The parser, used to interpret the search result.
+    /// The parser, used to interpret the search result.
     parser: SearchResultParser,
 }
 

src/engines/search_result_parser.rs

@@ -7,10 +7,15 @@ use scraper::{html::Select, ElementRef, Html, Selector};
 
 /// A html search result parser, based on a predefined CSS selectors.
 pub struct SearchResultParser {
+    /// selector to locate the element which is displayed, if there were nothing found.
     no_result: Selector,
+    /// selector to locate the element which contains one item from the search result.
     results: Selector,
+    /// selector to locate the title relative to the search result item.
     result_title: Selector,
+    /// selector to locate the url relative to the search result item.
     result_url: Selector,
+    /// selector to locate the description relative to the search result item.
     result_desc: Selector,
 }
 

src/engines/searx.rs

@@ -14,7 +14,7 @@ use error_stack::{Report, Result, ResultExt};
 /// A new Searx engine type defined in-order to implement the `SearchEngine` trait which allows to
 /// reduce code duplication as well as allows to create vector of different search engines easily.
 pub struct Searx {
-    // The parser, used to interpret the search result.
+    /// The parser, used to interpret the search result.
     parser: SearchResultParser,
 }