Add small help section to README.md

Author: siffiejoe

README.md

@@ -26,3 +26,28 @@ changes to the original lua-getsize code:
     (the default), "u" will count Lua upvalues (the default), and "U"
     will _not_ count Lua upvalues. You can combine those options.
 
+##                          Getting Started                         ##
+
+
+This module exports just one function:
+
+```lua
+local getsize = require("getsize")
+```
+
+Calling this function with a Lua value as argument will return the
+size of the value in bytes. For tables it will return the lengths of
+array and hash part as additional return values. For functions you can
+decide whether you want to include the sizes of the proto object
+and/or the upvalues.
+
+```lua
+print(getsize(getsize))                    # -> 64
+local function f() return getsize end
+print(getsize(f))                          # -> 80
+print(getsize(f, "uP"))                    # -> 80
+print(getsize(f, "up"))                    # -> 264
+print(getsize(f, "UP"))                    # -> 40
+print(getsize({ 1, 2, 3, x = 4, y = 5 })   # -> 152  3  2
+```
+