Updated Directive (markdown)

Directive.md

@@ -1,3 +1,5 @@
+# ShellCheck Directives
+
 Shellcheck directives allow you to control how `shellcheck` works, and take the form of comments in files:
 
 ```sh
@@ -7,6 +9,18 @@ hexToAscii() {
 }
 ```
 
+or entries in a `.shellcheckrc` in the project root or user's home directory:
+
+```none
+$ cat ~/.shellcheckrc
+
+# Don't suggest [ -n "$VAR" ] over [ ! -z "$VAR" ] 
+disable=SC2236
+
+# Suggest ${VAR} in place of $VAR
+enable=require-variable-braces
+```
+
 ## Supported directives
 
 ### disable
@@ -23,6 +37,18 @@ A range of errors can also be specified, handy when disbaling things for the ent
 # shellcheck disable=SC1000-SC9999
 ```
 
+### enable
+
+Enables an [[optional]] check (since 0.7.0).
+
+```sh
+#!/bin/bash
+# shellcheck enable=require-variable-braces
+echo "Hello $USER"  # Will suggest ${USER}
+```
+
+To see a list of optional checks with examples, run `shellcheck --list-optional`. See [[here|optional]] for more information.
+
 ### source
 Tell ShellCheck where to find a sourced file (since 0.4.0):