Rewritten README, added screenshots

README.md

-mapfix
-======
+#mapfix
 
 Fix some map errors (flow and light problems)
+
+![Before](http://i.imgur.com/T3csYME.png)
+![After](http://i.imgur.com/d0V0aO7.png)
+Look at the water and the jungle trunk at the center.
+
+
+##minetest.conf settings
+* mapfix_default_size (by default 40) : size used when omitted
+* mapfix_max_size (by default 50) : maximum size allowed for players
+* mapfix_delay (by default 15) : minimal delay in seconds between 2 "/mapfix" (to avoid server freezing)
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