Merge pull request #478 from miparnisari/patch-1

Properly highlight code snippets in documentation

custom_rule_development.md

@@ -1,38 +1,44 @@
 ## Crash Course in (New) Rule Development
 
 1. Create a class that ends with the name Rule.  This is a convention that must be observed in order for cfn-nag to load
-   the rule.  Additionally, derive this class from BaseRule:
+   the rule. Additionally, derive this class from `BaseRule`:
 
-        require 'cfn-nag/violation'
-        require_relative 'base'
+     ```ruby
+     require 'cfn-nag/violation'
+     require_relative 'base'
 
-        class IamManagedPolicyNotActionRule < BaseRule
+     class IamManagedPolicyNotActionRule < BaseRule
+     ```
 
 2. Define methods that describe some of the bookkeeping for the rule, like whether it is a WARNING/FAILING_VIOLATION, its
    unique identifier among rules, and error text shown when it matches:
 
-        def rule_text
-          'IAM managed policy should not allow Allow+NotAction'
-        end
+      ```ruby
+     def rule_text
+       'IAM managed policy should not allow Allow+NotAction'
+     end
 
-        def rule_type
-          Violation::WARNING
-        end
+     def rule_type
+       Violation::WARNING
+     end
 
-        def rule_id
-          'W17'
-        end
+     def rule_id
+       'W17'
+     end
+    ```
 
 3. Define the `audit_impl` method to do the actual work of the analysis.  This method should return an array of
    logical resource identifiers from the CloudFormation template:
 
-        def audit_impl(cfn_model)
-          violating_policies = cfn_model.resources_by_type('AWS::IAM::ManagedPolicy').select do |policy|
-            !policy.policy_document.allows_not_action.empty?
-          end
+     ```ruby
+     def audit_impl(cfn_model)
+       violating_policies = cfn_model.resources_by_type('AWS::IAM::ManagedPolicy').select do |policy|
+         !policy.policy_document.allows_not_action.empty?
+       end
 
-          violating_policies.map { |policy| policy.logical_resource_id }
-        end
+       violating_policies.map { |policy| policy.logical_resource_id }
+     end
+     ```
 
 4. The cfn_model object passed into the `audit_impl` method is where a majority of the improvement lies.  When
    a CloudFormation document is parsed, it is mapped into a collection of objects that mirror the resource types.
@@ -43,13 +49,15 @@
      * Attributes/properties are returned in camelCase.
      * For example, if dealing with an object type of 'AWS::RDS::DBCluster', and needing to write logic against the 'StorageEncrypted' property, then an example `audit_impl` might look like this:
 
+          ```ruby
            def audit_impl(cfn_model)
              violating_rdscluster = cfn_model.resources_by_type('AWS::RDS::DBCluster').select do |cluster|
                cluster.storageEncrypted.nil? || cluster.storageEncrypted.to_s.downcase == 'false'
              end
 
              violating_rdscluster.map { |cluster| cluster.logical_resource_id }
            end
+          ```
 
    * cfn-model provides special handling for a subset of objects whereby properties may be transformed into something
      simpler and/or objects may be linked together.  
@@ -114,4 +122,4 @@ install` to install dependencies.
 
 For any generic rules you want to share with the community, submit a PR of the rule to `lib/custom_rules`. 
 Code should be linted using [Rubocop](https://github.com/rubocop-hq/rubocop).  Please be sure to use a unique 
-`rule_id` and write the rule according section 1 of the above "Where to Place Rule Files" area.
+`rule_id` and write the rule according section 1 of the above "Where to Place Rule Files" area.