Improve readme file

Link wiki API page, clean compatibility notes a bit, fix formatting.

README.md

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 Citizens2 README
 ================
 
-Citizens is an NPC plugin for the Bukkit API. It was first released on March 5, 2011, and has since seen numerous updates. Citizens provides an API which developers can use to create their own NPC characters. More information on the API can be found at its repository (https://github.com/CitizensDev/CitizensAPI).
+Citizens is an NPC plugin for the Bukkit API. It was first released on March 5, 2011, and has since seen numerous updates. Citizens provides an API which developers can use to create their own NPC characters. More information on the API can be found on the API page of the Citizens Wiki (https://wiki.citizensnpcs.co/API).
 
 Compatible with:
-* Minecraft (see http://wiki.citizensnpcs.co/Versions for info)
-* CitizensAPI
+* Minecraft (for specific compatible version information, see http://wiki.citizensnpcs.co/Versions for info)
+* CitizensAPI (for compiling purposes only)
 
 Extra information
 =================
+
 Javadoc: http://jd.citizensnpcs.co
+
 Spigot page: https://www.spigotmc.org/resources/citizens.13811
+
 For questions/help join our discord at: https://discord.gg/Q6pZGSR