doc: improve Buffer() text

Rewording, punctuation, consistent sentence structure and italics, wrap
section at 80 characters.

PR-URL: https://github.com/nodejs/node/pull/19567
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

doc/api/buffer.md

@@ -52,28 +52,27 @@ In versions of Node.js prior to 6.0.0, `Buffer` instances were created using the
 `Buffer` constructor function, which allocates the returned `Buffer`
 differently based on what arguments are provided:
 
-* Passing a number as the first argument to `Buffer()` (e.g. `new Buffer(10)`),
+* Passing a number as the first argument to `Buffer()` (e.g. `new Buffer(10)`)
   allocates a new `Buffer` object of the specified size. Prior to Node.js 8.0.0,
   the memory allocated for such `Buffer` instances is *not* initialized and
   *can contain sensitive data*. Such `Buffer` instances *must* be subsequently
   initialized by using either [`buf.fill(0)`][`buf.fill()`] or by writing to the
-  `Buffer` completely. While this behavior is *intentional* to improve
-  performance, development experience has demonstrated that a more explicit
-  distinction is required between creating a fast-but-uninitialized `Buffer`
-  versus creating a slower-but-safer `Buffer`. Starting in Node.js 8.0.0,
-  `Buffer(num)` and `new Buffer(num)` will return a `Buffer` with initialized
-  memory.
+  entire `Buffer`. While this behavior is *intentional* to improve performance,
+  development experience has demonstrated that a more explicit distinction is
+  required between creating a fast-but-uninitialized `Buffer` versus creating a
+  slower-but-safer `Buffer`. Starting in Node.js 8.0.0,  `Buffer(num)` and
+  `new Buffer(num)` will return a `Buffer` with initialized memory.
 * Passing a string, array, or `Buffer` as the first argument copies the
   passed object's data into the `Buffer`.
 * Passing an [`ArrayBuffer`] or a [`SharedArrayBuffer`] returns a `Buffer` that
   shares allocated memory with the given array buffer.
 
 Because the behavior of `new Buffer()` is different depending on the type of the
-first argument, security and reliability issues can be inadvertantly introduced
-into applications when argument validation or `Buffer` initialization are not
+first argument, security and reliability issues can be inadvertently introduced
+into applications when argument validation or `Buffer` initialization is not
 performed.
 
-To make the creation of `Buffer` instances more reliable and less error prone,
+To make the creation of `Buffer` instances more reliable and less error-prone,
 the various forms of the `new Buffer()` constructor have been **deprecated**
 and replaced by separate `Buffer.from()`, [`Buffer.alloc()`], and
 [`Buffer.allocUnsafe()`] methods.
@@ -81,24 +80,25 @@ and replaced by separate `Buffer.from()`, [`Buffer.alloc()`], and
 *Developers should migrate all existing uses of the `new Buffer()` constructors
 to one of these new APIs.*
 
-* [`Buffer.from(array)`] returns a new `Buffer` containing a *copy* of the provided
-  octets.
+* [`Buffer.from(array)`] returns a new `Buffer` that *contains a copy* of the
+  provided octets.
 * [`Buffer.from(arrayBuffer[, byteOffset [, length]])`][`Buffer.from(arrayBuffer)`]
-  returns a new `Buffer` that *shares* the same allocated memory as the given
+  returns a new `Buffer` that *shares the same allocated memory* as the given
   [`ArrayBuffer`].
-* [`Buffer.from(buffer)`] returns a new `Buffer` containing a *copy* of the
+* [`Buffer.from(buffer)`] returns a new `Buffer` that *contains a copy* of the
   contents of the given `Buffer`.
-* [`Buffer.from(string[, encoding])`][`Buffer.from(string)`] returns a new `Buffer`
-  containing a *copy* of the provided string.
-* [`Buffer.alloc(size[, fill[, encoding]])`][`Buffer.alloc()`] returns a "filled"
-  `Buffer` instance of the specified size. This method can be significantly
-  slower than [`Buffer.allocUnsafe(size)`][`Buffer.allocUnsafe()`] but ensures
-  that newly created `Buffer` instances never contain old and potentially
-  sensitive data.
+* [`Buffer.from(string[, encoding])`][`Buffer.from(string)`] returns a new
+  `Buffer` that *contains a copy* of the provided string.
+* [`Buffer.alloc(size[, fill[, encoding]])`][`Buffer.alloc()`] returns a new
+  initialized `Buffer` of the specified size. This method is slower than
+  [`Buffer.allocUnsafe(size)`][`Buffer.allocUnsafe()`] but guarantees that newly
+  created `Buffer` instances never contain old data that is potentially
+  sensitive.
 * [`Buffer.allocUnsafe(size)`][`Buffer.allocUnsafe()`] and
   [`Buffer.allocUnsafeSlow(size)`][`Buffer.allocUnsafeSlow()`] each return a
-  new `Buffer` of the specified `size` whose content *must* be initialized
-  using either [`buf.fill(0)`][`buf.fill()`] or written to completely.
+  new uninitialized `Buffer` of the specified `size`. Because the `Buffer` is
+  uninitialized, the allocated segment of memory might contain old data that is
+  potentially sensitive.
 
 `Buffer` instances returned by [`Buffer.allocUnsafe()`] *may* be allocated off
 a shared internal memory pool if `size` is less than or equal to half
@@ -117,7 +117,7 @@ force all newly allocated `Buffer` instances created using either
 this flag *changes the default behavior* of these methods and *can have a significant
 impact* on performance. Use of the `--zero-fill-buffers` option is recommended
 only when necessary to enforce that newly allocated `Buffer` instances cannot
-contain potentially sensitive data.
+contain old data that is potentially sensitive.
 
 ```txt
 $ node --zero-fill-buffers