docs: Reference all the documentation from index.md.

README.md

 
 ## Documentation
 
-The [main documentation](docs/index.md) for eSpeak NG provides more information
-on using and creating voices/languages for eSpeak NG.
+The [documentation](docs/index.md) for eSpeak NG provides:
+
+1.  a user guide;
+2.  a guide for language and voice authors; and
+3.  details for developers.
 
 The [espeak-ng](src/espeak-ng.1.ronn) and [speak-ng](src/speak-ng.1.ronn)
 command-line documentation provide a reference of the different command-line

docs/index.md

 
 - [Features](#features)
 - [History](#history)
-- [Adding or Improving a Language](add_language.md)
-  - [Text to Phoneme Translation](dictionary.md)
-- [Voice Files](voices.md)
-  - [MBROLA Voices](mbrola.md)
-  - [Phoneme Tables](phontab.md)
-- [Intonation](intonation.md)
-- [SSML and HTML Support](markup.md)
+- User Guide
+  - [espeak-ng Command Line](../src/espeak-ng.1.ronn)
+  - [speak-ng Command Line](../src/speak-ng.1.ronn)
+  - [Supported Languages](languages.md)
+  - [SSML and HTML Support](markup.md)
+- Creating and Editing Languages and Voices
+  - [Adding or Improving a Language](add_language.md)
+    - [Text to Phoneme Translation](dictionary.md)
+  - [Voice Files](voices.md)
+    - [MBROLA Voices](mbrola.md)
+    - [Phoneme Tables](phontab.md)
+  - [Intonation](intonation.md)
+- Phonemes
+  - [Phoneme Features and the International Phonetic Alphabet](phonemes.md)
+    - [Kirshenbaum (ASCII-IPA) Transcription Scheme](phonemes/kirshenbaum.md)
+    - [X-SAMPA Transcription Scheme](phonemes/xsampa.md)
+    - [Conlang X-SAMPA Transcription Scheme](phonemes/cxs.md)
+  - [Phoneme Model](phoneme_model.md)
+  - Pronunciation Guides
+    - [English](languages/gmw/en.md)
 - [License](../COPYING)
 
 ----------

docs/languages.md

 | `zlw`       | `cs`              | West Slavic           | Czech                       |                        |
 | `gmq`       | `da`              | North Germanic        | Danish                      |                        |
 | `gmw`       | `nl`              | West Germanic         | Dutch                       |                        |
-| `gmw`       | `en-US`           | West Germanic         | [English](languages/gmw/en.md)  | American               |
-| `gmw`       | `en`              | West Germanic         | [English](languages/gmw/en.md)  | British                |
-| `gmw`       | `en-029`          | West Germanic         | [English](languages/gmw/en.md)  | Caribbean              |
-| `gmw`       | `en-GB-x-gbclan`  | West Germanic         | [English](languages/gmw/en.md)  | Lancastrian            |
-| `gmw`       | `en-GB-x-rp`      | West Germanic         | [English](languages/gmw/en.md)  | Received Pronunciation |
-| `gmw`       | `en-GB-scotland`  | West Germanic         | [English](languages/gmw/en.md)  | Scottish               |
-| `gmw`       | `en-GB-x-gbcwmd`  | West Germanic         | [English](languages/gmw/en.md)  | West Midlands          |
+| `gmw`       | `en-US`           | West Germanic         | English                     | American               |
+| `gmw`       | `en`              | West Germanic         | English                     | British                |
+| `gmw`       | `en-029`          | West Germanic         | English                     | Caribbean              |
+| `gmw`       | `en-GB-x-gbclan`  | West Germanic         | English                     | Lancastrian            |
+| `gmw`       | `en-GB-x-rp`      | West Germanic         | English                     | Received Pronunciation |
+| `gmw`       | `en-GB-scotland`  | West Germanic         | English                     | Scottish               |
+| `gmw`       | `en-GB-x-gbcwmd`  | West Germanic         | English                     | West Midlands          |
 | `art`       | `eo`              | Constructed           | Esperanto                   |                        |
 | `urj`       | `et`              | Uralic                | Estonian                    |                        |
 | `ira`       | `fa`              | Iranian               | Persian                     |                        |

docs/phonemes.md

-# Phonemes
+# Phoneme Features and the International Phonetic Alphabet
 
 - [Phoneme Transcription Schemes](#phoneme-transcription-schemes)
 - [Consonants](#consonants)