docs: streamline nav and page structure

- Separate nav items instead of single include-based page
- Merge description.adoc content into index.adoc
- Remove licence.adoc, add inline license to index.adoc
- Fix markdown fenced blocks to AsciiDoc source blocks
- Add installation.adoc to nav
- Change nav label from Start to Overview

Signed-off-by: jimisola <jimisola@jimisola.com>

Author: Jimisola Laursen

docs/modules/ROOT/nav.adoc

@@ -1,2 +1,3 @@
-* xref:index.adoc[Start]
-* xref:usage.adoc[Usage]
+* xref:index.adoc[Overview]
+* xref:installation.adoc[Installation]
+* xref:usage.adoc[Usage]

docs/modules/ROOT/pages/description.adoc

@@ -1,7 +1,7 @@
 = Reqstool Python Decorators
 
-include::description.adoc[]
+This provides decorators and collecting of decorated code, formatting it and writing to yaml file.
 
-include::installation.adoc[]
+== License
 
-include::licence.adoc[]
+MIT License.

docs/modules/ROOT/pages/index.adoc

@@ -2,8 +2,7 @@
 
 The package name is `reqstool-python-decorators`.
 
-* Using pip:
-
-```
+[source,bash]
+----
 pip install reqstool-python-decorators
-```
+----

docs/modules/ROOT/pages/installation.adoc

@@ -4,54 +4,60 @@
 
 * Hatch
 
-```
+[source,toml]
+----
 dependencies = [
     "reqstool-python-decorators == <version>"
 ]
-```
+----
 
 * Poetry
 
-```
+[source,toml]
+----
 [tool.poetry.dependencies]
 reqstool-python-decorators = "<version>"
-```
+----
 
 === Decorators
 
 Import decorators:
 
-```
+[source,python]
+----
 from reqstool_python_decorators.decorators.decorators import Requirements, SVCs
-```
+----
 
 Example usage of the decorators:
 
-```python
+[source,python]
+----
 @Requirements("REQ_111", "REQ_222")
 def somefunction():
-```
+----
 
-```python
+[source,python]
+----
 @SVCs("SVC_111", "SVC_222")
 def test_somefunction():
-```
+----
 
 === Processor
 
 Import processor:
 
-```
+[source,python]
+----
 from reqstool_python_decorators.processors.decorator_processor import DecoratorProcessor
-```
+----
 
 Main function to collect decorators data and generate yaml file:
 
-```
+[source,python]
+----
 process_decorated_data(path_to_python_files, output_file)
-```
+----
 
 `path_to_python_files` is the directories to search through to find decorated code.
 
 (Optional) `output_file` is output file(path) the yaml file is stored to. Default is `/build/reqstool/annotations.yml`.
-