docs: tiny style improvements

doc/contributing.rst

@@ -252,6 +252,7 @@ the imperative (command) form. That is, between:
   proc hello*(): string =
     ## Return "hello"
     result = "hello"
+
 or
 
 .. code-block:: nim

doc/manual.rst

@@ -4140,7 +4140,7 @@ A custom exception is a custom type:
 .. code-block:: nim
   type
     LoadError* = object of Exception
-  
+
 Ending the custom exception's name with ``Error`` is recommended.
 
 Custom exceptions can be raised like any others, e.g.:
@@ -6504,7 +6504,7 @@ alignment requirement of the type are ignored.
 
    type
      sseType = object
-       sseData {.align(16).}: array[4,float32]
+       sseData {.align(16).}: array[4, float32]
 
      # every object will be aligned to 128-byte boundary
      Data = object