doc: improve process & os docs to give descriptive information about the platform property

Author: twitharshil

doc/api/os.md

@@ -301,7 +301,7 @@ added: v0.5.0
 
 * Returns: {string}
 
-Returns a string identifying the operating system platform. The value is set
+Returns a string identifying the operating system platform for which the Node.js binary was compiled. The value is set
 at compile time. Possible values are `'aix'`, `'darwin'`, `'freebsd'`,
 `'linux'`, `'openbsd'`, `'sunos'`, and `'win32'`.
 

doc/api/process.md

@@ -2612,8 +2612,7 @@ added: v0.1.16
 
 * {string}
 
-The `process.platform` property returns a string identifying the operating
-system platform on which the Node.js process is running.
+The `process.platform` property returns a string identifying the operating system platform for which the Node.js binary was compiled.
 
 Currently possible values are: