Make filepath links in readme relative (#4509)

This allows programs like emacs to open the proper file when
clicking them.

Co-authored-by: binarycat <binarycat@envs.net>

README.md

@@ -14,11 +14,11 @@ Based off RHH's pokeemerald-expansion v1.8.0 https://github.com/rh-hideout/pokee
 
 ## What features are included?
 - ***IMPORTANT*❗❗ Read through these to learn what features you can toggle**:
-    - [Battle configurations](/include/config/battle.h)
-    - [Pokémon configurations](/include/config/pokemon.h)
-    - [Item configurations](/include/config/item.h)
-    - [Overworld configurations](/include/config/overworld.h)
-    - [Debug configurations](/include/config/debug.h)
+    - [Battle configurations](include/config/battle.h)
+    - [Pokémon configurations](include/config/pokemon.h)
+    - [Item configurations](include/config/item.h)
+    - [Overworld configurations](include/config/overworld.h)
+    - [Debug configurations](include/config/debug.h)
 - ***Upgraded battle engine.***
     - Gen5+ damage calculation.
     - 2v2 Wild battles support.
@@ -62,7 +62,7 @@ Based off RHH's pokeemerald-expansion v1.8.0 https://github.com/rh-hideout/pokee
     - Recalculating stats at the end of every battle.
     - Level 100 Pokémon can earn EVs.
     - Inverse battle support.
-    - TONS of other features listed [here](/include/config/battle.h).
+    - TONS of other features listed [here](include/config/battle.h).
 - ***Full Trainer customization***
     - Nickname, EVs, IVs, moves, ability, ball, friendship, nature, gender, shininess.
     - Custom tag battle support (teaming up an NPC in a double battle).
@@ -94,7 +94,7 @@ Based off RHH's pokeemerald-expansion v1.8.0 https://github.com/rh-hideout/pokee
     - All gender differences.
         - Custom female icons for female Hippopotas Hippowdon, Pikachu and Wobbufett
     - 3 Perfect IVs on Legendaries, Mythicals and Ultra Beasts.
-- ***Customizable form change tables. Full list of methods [here](/include/constants/form_change_types.h).***
+- ***Customizable form change tables. Full list of methods [here](include/constants/form_change_types.h).***
     - Item holding (eg. Giratina/Arceus)
     - Item using (eg. Oricorio)
         - Time of day option for Shaymin
@@ -115,7 +115,7 @@ Based off RHH's pokeemerald-expansion v1.8.0 https://github.com/rh-hideout/pokee
     - Egg Move Transfer, including Mirror Herb (configurable).
     - Nature inheriting 100% of the time with Everstone (configurable)
     - Gen6+ Ability inheriting (configurable).
-- ***Items from newer Generations. Full list [here](/include/constants/items.h).***
+- ***Items from newer Generations. Full list [here](include/constants/items.h).***
     - ***Gen 6+ Exp. Share*** (configurable)
     - Berserk Gene
     - Most battle items from Gen 4+