update docs

docs/modders/Entities_Format/Spell_School_Format.md

@@ -5,10 +5,14 @@ WARNING: currently custom spell schools are only partially supported:
 - it is possible to use custom spell schools in bonus system
 - it is possible to make skill for specializing in such spell
 - it is possible to specify border decorations for mastery level of such spell in spellbook
+- it is possible to set bookmarks and header image for spellbook
 
 ```json
 	// Internal field for H3 schools. Do not use for mods
 	"index" : "",
+
+	// name of the school
+	"name" : "",
 	
 	// animation file with spell borders for spell mastery levels
 	"schoolBorders" : "SplevA",