[docs] flake8-self Private member access docs (#2912)

crates/ruff/src/rules/flake8_self/rules/private_member_access.rs

@@ -9,6 +9,42 @@ use crate::registry::Diagnostic;
 use crate::violation::Violation;
 
 define_violation!(
+    /// ## What it does
+    /// Checks for accesses on "private" class members.
+    ///
+    /// ## Why is this bad?
+    /// In Python, the convention is such that class members that are prefixed
+    /// with a single underscore, or prefixed but not suffixed with a double
+    /// underscore, are considered private and intended for internal use.
+    ///
+    /// Using such "private" members is considered a misuse of the class, as
+    /// there are no guarantees that the member will be present in future
+    /// versions, that it will have the same type, or that it will have the same
+    /// behavior. Instead, use the class's public interface.
+    ///
+    /// ## Example
+    /// ```python
+    /// class Class:
+    ///     def __init__(self):
+    ///         self._private_member = "..."
+    ///
+    /// var = Class()
+    /// print(var._private_member)
+    /// ```
+    ///
+    /// Use instead:
+    /// ```python
+    /// class Class:
+    ///     def __init__(self):
+    ///         self.public_member = "..."
+    ///
+    /// var = Class()
+    /// print(var.public_member)
+    /// ```
+    ///
+    /// ## References
+    /// * [_What is the meaning of single or double underscores before an object name?_](https://stackoverflow.com/questions/1301346/what-is-the-meaning-of-single-and-double-underscore-before-an-object-name)
+    /// ```
     pub struct PrivateMemberAccess {
         pub access: String,
     }