fix headings in readmes

subjects/action-reaction/README.md

@@ -1,4 +1,4 @@
-### Action - reaction!
+### Instructions
 
 OK, you have now connected HTML, CSS and JS altogether ; big day! Excited? Exhausted?
 Well so far, you've only scratched the surface... Let's go deeper into the power of JS! You're going to add some interaction ; the webpage will react when a user action will happen, called an [event](https://developer.mozilla.org/en-US/docs/Web/Events) (a click, a key pressed, a mouse move, etc.).

subjects/bring-it-to-life/README.md

@@ -1,4 +1,4 @@
-### Bring it to life
+### Instructions
 
 Still there? Well done! But hold on, here begins the serious part... In order to control your creation, you're going to plug its brain: JavaScript.
 

subjects/class-that/README.md

@@ -1,4 +1,4 @@
-### Class that
+### Instructions
 
 Alright, your being is almost done, some elements still need a bit more shaping and then we'll make it come to life!
 If you look at your page, you can observe that some elements come by pair: the eyes, the arms & the legs. It is the same organ, one on the left and one on the right ; they have exactly the same shape, so for practicity & to avoid to repeat twice the same style, we're not going to use their `id` to style them, but a [`class`](https://developer.mozilla.org/en-US/docs/Web/CSS/Class_selectors) ; contrary to an `id`, a `class` can be attributed to several different elements with common rulesets, and so the style defined for that class will apply to all the HTML elements that have it.

subjects/first-words/README.md

@@ -1,4 +1,4 @@
-### First words
+### Instructions
 
 Now that you know how to make your creation move, what about making it communicate its first words to the world?
 

subjects/nesting-organs/README.md

@@ -1,4 +1,4 @@
-### Nesting organs
+### Instructions
 
 Bravo! You displayed the global shape of your entity, but now it's time to populate each division ; let's add up some organs!
 To do so, we're going to introduce you the concept of nesting elements inside others.

subjects/select-and-style/README.md

@@ -1,5 +1,3 @@
-## Select & style
-
 ### Instructions
 
 Now that you created & identified properly the different sections of your being,
@@ -8,6 +6,7 @@ style it with [CSS][0]. Create a CSS file, [link it][1] to your
 `select-and-style.html`, and:
 
 - target all the elements with the [universal selector][2] and style them with:
+
   - `margin` of `0`
   - `box-sizing` to `border-box`
   - `opacity` of `0.85`
@@ -16,6 +15,7 @@ style it with [CSS][0]. Create a CSS file, [link it][1] to your
   viewport height
 
 - target all the `section` tags with the [type selector][3], and style it with:
+
   - `padding` of `20px`
   - `width` of `100%`
   - `height` of `calc(100% / 3)` _(one third of the `body` height)_

subjects/skeleton/README.md

@@ -1,6 +1,4 @@
-### Skeleton
+### Instructions
-
-#### Instructions
 
 Welcome to the `world-wide-what` quest!
 In this new digital world you're gonna discover, it is possible to create beings with some lines of code. Yes, it is.

subjects/the-calling/README.md

@@ -1,11 +1,9 @@
-## The calling
+### Instructions
 
 Congrats! You created the very first base for your being and you witnessed its
 appearance on the digital world - your browser. But so far, it's a tiny seed of
 the marvelous thing it could become ; be patient, there still is a bit of work.
 
-### Instructions
-
 First of all, instead of writing down what things are _(you're not writing down
 on your hand the word 'hand', are you?)_ we're going to identify them
 semantically with the very practical