Add guides on Getting Started with JS (#4150)

- Get started section added to the JS docs
- Small fixes in the JS modules docs

documentation/js/js_gpio.md

@@ -1,14 +1,12 @@
-# js_gpio {#js_gpio}
+# GPIO module {#js_gpio}
+
+The module allows you to control GPIO pins of the expansion connector on Flipper Zero. Call the `require` function to load the module before first using its methods. This module depends on the `event_loop` module, so it **must** be imported after `event_loop` is imported:
 
-# GPIO module
 ```js
 let eventLoop = require("event_loop");
 let gpio = require("gpio");
 ```
 
-This module depends on the `event_loop` module, so it _must_ only be imported
-after `event_loop` is imported.
-
 # Example
 ```js
 let eventLoop = require("event_loop");
@@ -31,11 +29,11 @@ Gets a `Pin` object that can be used to manage a pin.
   - `pin`: pin identifier (examples: `"pc3"`, `7`, `"pa6"`, `3`)
 
 ### Returns
-A `Pin` object
+A `Pin` object.
 
 ## `Pin` object
 ### `Pin.init()`
-Configures a pin
+Configures a pin.
 
 #### Parameters
   - `mode`: `Mode` object:
@@ -49,28 +47,28 @@ Configures a pin
     - `pull` (optional): either `"up"`, `"down"` or unset
 
 ### `Pin.write()`
-Writes a digital value to a pin configured with `direction: "out"`
+Writes a digital value to a pin configured with `direction: "out"`.
 
 #### Parameters
   - `value`: boolean logic level to write
 
 ### `Pin.read()`
 Reads a digital value from a pin configured with `direction: "in"` and any
-`inMode` except `"analog"`
+`inMode` except `"analog"`.
 
 #### Returns
 Boolean logic level
 
 ### `Pin.readAnalog()`
 Reads an analog voltage level in millivolts from a pin configured with
-`direction: "in"` and `inMode: "analog"`
+`direction: "in"` and `inMode: "analog"`.
 
 #### Returns
-Voltage on pin in millivolts
+Voltage on pin in millivolts.
 
 ### `Pin.interrupt()`
 Attaches an interrupt to a pin configured with `direction: "in"` and
-`inMode: "interrupt"` or `"event"`
+`inMode: "interrupt"` or `"event"`.
 
 #### Returns
 An event loop `Contract` object that identifies the interrupt event source. The