feature #3901 Bootstraped the standards for "Files and Directories" (javiereguiluz)

This PR was merged into the 2.3 branch.

Discussion
----------

Bootstraped the standards for "Files and Directories"

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | -

This is just a draft. I really need your comments and suggestions to decide the best standards for this.

Commits
-------

a107884 Added some suggestions and fixed one minor formatting issue
7843fe6 Bootstraped the standards for "Files and Directories"

Author: weaverryan

contributing/documentation/standards.rst

@@ -81,6 +81,23 @@ Configuration examples should show all supported formats using
 * **Validation**: YAML, Annotations, XML, PHP
 * **Doctrine Mapping**: Annotations, YAML, XML, PHP
 
+Files and Directories
+~~~~~~~~~~~~~~~~~~~~~
+
+* When referencing directories, always add a trailing slash to avoid confusions
+  with regular files (e.g. *"execute the ``console`` script located at the ``app/``
+  directory"*).
+* When referencing file extensions explicitly, you should include a leading dot
+  for every extension (e.g. "*XML files use the ``.xml`` extension*").
+* When you list a Symfony file/directory hierarchy, use ``your-project/`` as the
+  top level directory. E.g.
+
+      your-project/
+      ├─ app/
+      ├─ src/
+      ├─ vendor/
+      └─ ...
+
 Example
 ~~~~~~~
 
@@ -128,11 +145,11 @@ Language Standards
 * When referencing a hypothetical person, such as "a user with a session cookie", gender-neutral
   pronouns (they/their/them) should be used. For example, instead of:
 
-     * he or she, use they
-     * him or her, use them
-     * his or her, use their
-     * his or hers, use theirs
-     * himself or herself, use themselves
+   * he or she, use they
+   * him or her, use them
+   * his or her, use their
+   * his or hers, use theirs
+   * himself or herself, use themselves
 
 .. _`the Sphinx documentation`: http://sphinx-doc.org/rest.html#source-code
 .. _`Twig Coding Standards`: http://twig.sensiolabs.org/doc/coding_standards.html