You have honed your ability to react to any situation, through training or some other way, that fits for your character. You gain the following benefits:

1. You gain proficiency in the acrobatics or perception skill.

2. You can now use the ready action as a bonus action on your turn instead of using an action. You can do so a number of times equal to half your proficiency bonus rounded up. If you ready a spell with your ready action, you gain advantage on saving throws against your concentration being broken.

If you take this feat again you gain the following benefits:

1. You gain proficiency in the other skill you didnt choose, or expertise in the skill you chose earlier.

2. You can use the ready action as a bonus action on your turn instead of using an action. You can do so a number of times equal to your proficiency bonus. If you ready a spell with your ready action, your concentration on the readied spell cant be broken.

For clarification, the 2nd effect of this feat, when you take it for the first and second time, only lasts until you cast the spell you ready. Example: 

Your ready the web spell using your bonus action. An enemy damages you using a ranged attack and your concentration on the readied web spell gets advantage on the saving throw, or cant be broken this way; then you cast it using your reaction, with the trigger being the damage from the enemy. The concentration on your web spell can be broken as normal, after you cast it.