Document how to supply docstrings to classes and class methods / lambdas

We want to encourage good practice, documentation-wise, amongst Hy
users!

docs/language/api.rst

@@ -814,6 +814,22 @@ function is defined and passed to another function for filtering output.
     Alice
     Dave
 
+Just as in normal function definitions, if the first element of the
+body is a string, it serves as docstring.  This is useful for giving
+class methods docstrings.
+
+    => (setv times-three
+    ...   (fn [x]
+    ...    "Multiplies input by three and returns the result."
+    ...    (* x 3)))
+
+    => (help times-three)
+    Help on function times_three:
+
+    times_three(x)
+    Multiplies input by three and returns result
+    (END)
+
 
 let
 ---

docs/tutorial.rst

@@ -436,10 +436,16 @@ Finally, of course we need classes!  In python we might have a class
 like::
 
   class FooBar(object):
+      """
+      Yet Another Example Class
+      """
       def __init__(self, x):
           self.x = x
 
       def get_x(self):
+          """
+          Return our copy of x
+          """
           return self.x
 
 
@@ -448,6 +454,7 @@ In Hy:
 .. code-block:: clj
 
   (defclass FooBar [object]
+    "Yet Another Example Class"
     [[--init--
       (fn [self x]
         (setv self.x x)
@@ -457,6 +464,7 @@ In Hy:
   
      [get-x
       (fn [self]
+        "Return our copy of x"
         self.x)]])