Update chapter_6.md

book/src/chapter_6.md

-# Chapter 5 - Fonts
+# Chapter 6 - Fonts
 Kayak UI uses SDF(signed distance fields) for rendering fonts. More specifically it uses multi-channel signed distance fields. Reasons for why we use MSDF:
 - High Quality font rendering.
 - Fast rendering!
@@ -25,4 +25,4 @@ Please refer to the documentation found in the link about for generating fonts.
 
 ```
 .\msdf-atlas-gen.exe -font .\my_font.ttf -type msdf -minsize 32 -format png -imageout my_font.png -json my_font.kayak_font
-```
+```
\ No newline at end of file