Update README with regex usage warning

Author: ManlyMarco

README.md

@@ -646,6 +646,8 @@ When creating manual translations, use this file as sparingly as you would use r
 ### Regex Usage
 Text translation files support regexes as well. Always remember to use regexes sparingly and scope them to avoid performance issues.
 
+**Warning:** Regexes can be placed in any file inside of the Text folder **except for all automatically generated files** that start with `_` (i.e. they won't work if placed inside `_AutoGeneratedTranslations.txt`).
+
 Regexes can be applied to translations in two different ways. The following two sections describes these two ways:
 
 #### Standard Regex Translation