doc: small clarifications to modules.markdown

per: nodejs/node-v0.x-archive#8708

A modified version of the original PR submitted by @builtbylane.

Reviewed By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
PR-URL: #2378

Author: jasnell

doc/api/modules.markdown

@@ -121,6 +121,8 @@ io.js has several modules compiled into the binary.  These modules are
 described in greater detail elsewhere in this documentation.
 
 The core modules are defined in io.js's source in the `lib/` folder.
+The core modules are defined within io.js's source and are located in the
+`lib/` folder.
 
 Core modules are always preferentially loaded if their identifier is
 passed to `require()`.  For instance, `require('http')` will always
@@ -131,22 +133,23 @@ return the built in HTTP module, even if there is a file by that name.
 <!--type=misc-->
 
 If the exact filename is not found, then io.js will attempt to load the
-required filename with the added extension of `.js`, `.json`, and then `.node`.
+required filename with the added extensions: `.js`, `.json`, and finally
+`.node`.
 
 `.js` files are interpreted as JavaScript text files, and `.json` files are
 parsed as JSON text files. `.node` files are interpreted as compiled addon
 modules loaded with `dlopen`.
 
-A module prefixed with `'/'` is an absolute path to the file.  For
+A required module prefixed with `'/'` is an absolute path to the file.  For
 example, `require('/home/marco/foo.js')` will load the file at
 `/home/marco/foo.js`.
 
-A module prefixed with `'./'` is relative to the file calling `require()`.
-That is, `circle.js` must be in the same directory as `foo.js` for
+A required module prefixed with `'./'` is relative to the file calling
+`require()`. That is, `circle.js` must be in the same directory as `foo.js` for
 `require('./circle')` to find it.
 
-Without a leading '/', './', or '../' to indicate a file, the module is either a
-core module or is loaded from a `node_modules` folder.
+Without a leading '/', './', or '../' to indicate a file, the module must
+either be a core module or is loaded from a `node_modules` folder.
 
 If the given path does not exist, `require()` will throw an Error with its
 `code` property set to `'MODULE_NOT_FOUND'`.