doc: add return types and props types to OS module

PR-URL: #9648
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/os.md

@@ -14,6 +14,8 @@ const os = require('os');
 added: v0.7.8
 -->
 
+* {String}
+
 A string constant defining the operating system-specific end-of-line marker:
 
 * `\n` on POSIX
@@ -35,6 +37,8 @@ Equivalent to [`process.arch`][].
 
 ## os.constants
 
+* {Object}
+
 Returns an object containing commonly used operating system specific constants
 for error codes, process signals, and so on. The specific constants currently
 defined are described in [OS Constants][].
@@ -44,6 +48,8 @@ defined are described in [OS Constants][].
 added: v0.3.3
 -->
 
+* Returns: {Array}
+
 The `os.cpus()` method returns an array of objects containing information about
 each CPU/core installed.
 
@@ -161,6 +167,8 @@ all processors are always 0.
 added: v0.9.4
 -->
 
+* Returns: {String}
+
 The `os.endianness()` method returns a string identifying the endianness of the
 CPU *for which the Node.js binary was compiled*.
 
@@ -174,6 +182,8 @@ Possible values are:
 added: v0.3.3
 -->
 
+* Returns: {Integer}
+
 The `os.freemem()` method returns the amount of free system memory in bytes as
 an integer.
 
@@ -182,6 +192,8 @@ an integer.
 added: v2.3.0
 -->
 
+* Returns: {String}
+
 The `os.homedir()` method returns the home directory of the current user as a
 string.
 
@@ -190,6 +202,8 @@ string.
 added: v0.3.3
 -->
 
+* Returns: {String}
+
 The `os.hostname()` method returns the hostname of the operating system as a
 string.
 
@@ -198,6 +212,8 @@ string.
 added: v0.3.3
 -->
 
+* Returns: {Array}
+
 The `os.loadavg()` method returns an array containing the 1, 5, and 15 minute
 load averages.
 
@@ -213,6 +229,8 @@ Windows platforms. On Windows, the return value is always `[0, 0, 0]`.
 added: v0.6.0
 -->
 
+* Returns: {Object}
+
 The `os.networkInterfaces()` method returns an object containing only network
 interfaces that have been assigned a network address.
 
@@ -272,6 +290,8 @@ The properties available on the assigned network address object include:
 added: v0.5.0
 -->
 
+* Returns: {String}
+
 The `os.platform()` method returns a string identifying the operating system
 platform as set during compile time of Node.js.
 
@@ -296,6 +316,8 @@ to be experimental at this time.
 added: v0.3.3
 -->
 
+* Returns: {String}
+
 The `os.release()` method returns a string identifying the operating system
 release.
 
@@ -308,6 +330,8 @@ https://en.wikipedia.org/wiki/Uname#Examples for more information.
 added: v0.9.9
 -->
 
+* Returns: {String}
+
 The `os.tmpdir()` method returns a string specifying the operating system's
 default directory for temporary files.
 
@@ -316,6 +340,8 @@ default directory for temporary files.
 added: v0.3.3
 -->
 
+* Returns: {Integer}
+
 The `os.totalmem()` method returns the total amount of system memory in bytes
 as an integer.
 
@@ -324,6 +350,8 @@ as an integer.
 added: v0.3.3
 -->
 
+* Returns: {String}
+
 The `os.type()` method returns a string identifying the operating system name
 as returned by uname(3). For example `'Linux'` on Linux, `'Darwin'` on OS X and
 `'Windows_NT'` on Windows.
@@ -336,6 +364,8 @@ information about the output of running uname(3) on various operating systems.
 added: v0.3.3
 -->
 
+* Returns: {Integer}
+
 The `os.uptime()` method returns the system uptime in number of seconds.
 
 *Note*: Within Node.js' internals, this number is represented as a `double`.
@@ -351,6 +381,7 @@ added: v6.0.0
  * `encoding` {String} Character encoding used to interpret resulting strings.
  If `encoding` is set to `'buffer'`, the `username`, `shell`, and `homedir`
  values will be `Buffer` instances. (Default: 'utf8')
+* Returns: {Object}
 
 The `os.userInfo()` method returns information about the currently effective
 user -- on POSIX platforms, this is typically a subset of the password file. The