AS OF v2.0.0, THE CONFIG GUIDE HAS BEEN MOVED TO https://github.com/JessebotX/StardewMods/tree/master/HealthStaminaRegen#configure
IF YOU ARE WONDERING WHERE THE CONFIG.JSON FILE IS, RUN THE GAME VIA SMAPI ONCE WITH THIS MOD INSTALLED FOR IT TO GENERATE

HealthRegenRate: 2 (the amount of health you get per second)
StaminaRegenRate: 2 (the amount of stamina you get per second)
SecondsUntilHealthRegen: 2 (if you took dmg, this number is the cooldown in seconds until you start regenerating again(must be a whole number, not 1.5 or etc.))
SecondsUntilStaminaRegen: 2 (if you used stamina, this number is the cooldown in seconds until you start regenerating again(must be a whole number, not 1.5 or etc.))