docs: add small section about xonsh and fix old style documentation (#60

)

README.md

@@ -34,7 +34,7 @@ This is an example of a configuration file:
 ```yaml
 version: 1.0.0
 groups:
-  - name: default
+  default:
     env-file: .env
     targets:
       clean:
@@ -107,3 +107,57 @@ If you have any problem, open an issue at: https://github.com/osl-incubator/maki
 
 As you can see, the help menu automatically adds information defined by all
 the `help` key, inside the `.makim.yaml` file.
+
+## Xonsh Shell Integration
+
+### What is Xonsh?
+[Xonsh](https://xon.sh/) is a powerful shell language and command prompt designed to
+seamlessly blend traditional shell capabilities with the expressive syntax of Python.
+  It offers an interactive and extensible environment that enables users to transition 
+  effortlessly between standard shell commands and Python scripting.
+
+### How Xonsh enhances this Project?
+In the context of this project, Xonsh serves as the default shell for executing commands 
+defined in the Makim configuration. By leveraging Xonsh, the Makim tool gains the flexibility 
+and richness of the Python programming language within a command-line interface. This integration 
+allows users to create sophisticated tasks and harness the full power of Python directly 
+in the terminal.
+
+### Key Features and Commands in Xonsh
+1. **Unified Syntax :** Xonsh seamlessly integrates traditional shell syntax with Python's 
+clean and expressive syntax, creating a unified and consistent scripting experience.
+```
+# Shell-style command
+ls -l
+
+# Python-style variable assignment
+$filename = "example.txt"
+
+# Combining both in a single command
+echo "The contents of $filename are: $(cat $filename)"
+```
+
+2. **Python Variables and Expressions :** Python variables can be easily incorporated into 
+commands, enhancing the readability and flexibility of your scripts.
+```
+$filename = "example.txt"
+echo "The filename is $filename"
+```
+
+3. **Looping and Conditional Statements :** Use Python-style loops and conditionals to create 
+dynamic and complex command sequences.
+```
+for $i in range(3):
+    echo "Iteration $i"
+```
+
+4. **Extensible Tab Completion :** Xonsh offers extensible and intelligent tab completion, 
+making it easier to discover and complete commands and variables.
+```
+$long_variable_name = "some_value"
+echo $long_<TAB>
+# Xonsh will intelligently complete the variable name
+```
+
+For more comprehensive information and documentation, explore the [Xonsh GitHub repository]
+(https://github.com/xonsh/xonsh) and the official [Xonsh website](https://xon.sh/).