doc: now we use init_by_lua_block {} instead of init_by_lua; also force a full GC cycle after loading resty.core.

Author: agentzh

README.markdown

@@ -49,9 +49,10 @@ Synopsis
  # are using the OpenResty bundle 1.4.3.9+.
  lua_package_path "/path/to/lua-resty-core/lib/?.lua;;";
 
- init_by_lua '
+ init_by_lua_block {
  require "resty.core"
- ';
+ collectgarbage("collect") -- just to collect any garbage
+ }
 
  ...
  }