add chapter [Docs and Comments]

practices/doc-comments/src/lib.rs

@@ -0,0 +1,54 @@
+//! # Doc comments
+//! 
+//! A library for showing how to use doc comments
+
+pub mod compute;
+
+/// Add one to the given value and return a new value
+///
+/// # Examples
+///
+/// ```
+/// let arg = 5;
+/// let answer = doc_comments::add_one(arg);
+///
+/// assert_eq!(6, answer);
+/// ```
+pub fn add_one(x: i32) -> i32 {
+    x + 1
+}
+
+
+
+/** Add two to the given value and return a new value
+
+# Examples
+
+```
+let arg = 5;
+let answer = doc_comments::add_two(arg);
+
+assert_eq!(7, answer);
+```
+*/
+pub fn add_two(x: i32) -> i32 {
+    x + 2
+}
+
+
+/// Add three to the given value and return a [`Option`] type
+pub fn add_three(x: i32) -> Option<i32> {
+    Some(x + 3)
+}
+
+mod a {
+    ///  Add four to the given value and return a [`Option`] type
+    /// [`crate::MySpecialFormatter`]
+    pub fn add_four(x: i32) -> Option<i32> {
+        Some(x + 4)
+    }
+}
+
+struct MySpecialFormatter;
+
+