Update fn docs and readability.

fn.nix

@@ -2,10 +2,34 @@
 with builtins;
 with lib;
 rec {
+  /**
+    Shorthand for "if condition then a else b"
+
+    # Type
+    ```
+    ifelse :: Bool -> Any -> Any -> Any
+    ```
+
+    # Arguments
+    - [condition] A condition evaluating to a boolean
+    - [a] Result if condition evaluates to true
+    - [b] Result if condition evaluates to false
+
+    # Example
+    ```nix
+    let
+      myData = { val = "custom"; };
+    in ifelse (myData ? val) myData.val "default"
+    => "custom"
+    ```
+  */
   ifelse =
-    a: b: c:
+    condition: a: b:
-    if a then b else c;
+    if condition then a else b;
-  fileContentsOr = a: b: (ifelse (pathIsRegularFile a) a b);
+
+  /**
+    Value of PWD environment variable at evaluation time
+  */
   cwd = builtins.getEnv "PWD";
 
   # lst (string PATH) (string FILETYPE) (bool RETURNFULLPATH)