Transform custom validation text into a folder

Author: alexander-yevsyukov

docs/content/docs/validation/01-getting-started/first-model.md

@@ -149,4 +149,4 @@ formatted shouldContain "wrong number"
 - Learn how Validation works internally:
   [Architecture](../09-developers-guide/architecture.md).
 - If you need organization-specific rules:
-  [Adding custom validation](../adding-custom-validation.md).
+  [Custom validation](../08-custom-validation/).

…s/validation/adding-custom-validation.md …alidation/08-custom-validation/_index.mddocs/content/docs/validation/adding-custom-validation.md renamed to docs/content/docs/validation/08-custom-validation/_index.md docs/content/docs/validation/adding-custom-validation.md renamed to docs/content/docs/validation/08-custom-validation/_index.md

@@ -1,4 +1,4 @@
-# Adding custom validation
+# Custom validation
 
 Users can extend the library by providing custom Protobuf options and code generation logic.
 
@@ -15,11 +15,11 @@ Follow these steps to create a custom option:
 
 Below is a workflow diagram for a typical option:
 
-![Typical custom option](.github/readme/typical_custom_option.jpg)
+![Typical custom option](../.github/readme/typical_custom_option.jpg)
 
 ## What’s next
 
-- Learn where this plugs in: [Architecture](09-developers-guide/architecture.md).
+- Learn where this plugs in: [Architecture](../09-developers-guide/architecture.md).
 
 Take a look at the `:java-tests:extensions` module that contains a full example of
 implementation of the custom `(currency)` option.

docs/content/docs/validation/09-developers-guide/architecture.md

@@ -18,4 +18,4 @@ The workflow is the following:
 ## What’s next
 
 - See the project layout: [Key modules](key-modules.md).
-- If you need organization-specific rules: [Adding custom validation](../adding-custom-validation.md).
+- If you need organization-specific rules: [Custom validation](../08-custom-validation/).

docs/content/docs/validation/09-developers-guide/key-modules.md

@@ -8,4 +8,4 @@
 
 ## What’s next
 
-- Build custom constraints: [Adding custom validation](../adding-custom-validation.md).
+- Build custom constraints: [Custom validation](../08-custom-validation/).

docs/content/docs/validation/_index.md

@@ -11,4 +11,4 @@ options, and runs those checks automatically when you build messages.
 ## Deeper topics
 
 - How it works: [Architecture](09-developers-guide/architecture.md)
-- Extension points: [Adding custom validation](adding-custom-validation.md)
+- Extension points: [Custom validation](08-custom-validation/)