Added gitbook variable for minimum version of python

Author: nikhiljohn10

book.json

@@ -3,6 +3,7 @@
     "variables": {
       "py_version": "3.9",
       "py_release": "3.9.0",
+      "py_min_version": "3.6.0",
       "pa_py_version": "3.8",
       "django_version": "2.2.4"
     },

en/python_installation/instructions.md

@@ -2,7 +2,7 @@
 
 > This section is based on a tutorial by Geek Girls Carrots (https://github.com/ggcarrots/django-carrots)
 
-Django is written in Python. We need Python to do anything in Django. Let's start by installing it! We want you to install the latest version of Python 3, so if you have any earlier version, you will need to upgrade it. If you already have version 3.4 or higher you should be fine.
+Django is written in Python. We need Python to do anything in Django. Let's start by installing it! We want you to install the latest version of Python 3, so if you have any earlier version, you will need to upgrade it. If you already have version {{ book.py_min_version }} or higher you should be fine.
 
 Please install normal Python as follows, even when you have Anaconda installed on your computer.
 
@@ -24,7 +24,7 @@ When the installation completes, you may see a dialog box with a link you can fo
 
 Note: if you are using an older version of Windows (7, Vista, or any older version) and the Python {{ book.py_version }}.x installer fails with an error, you can try either:
 1. install all Windows Updates and try to install Python again; or
-2. install an [older version of Python](https://www.python.org/downloads/windows/), e.g., [3.4.6](https://www.python.org/downloads/release/python-346/).
+2. install an [older version of Python](https://www.python.org/downloads/windows/), e.g., [{{ book.py_min_version }}](https://www.python.org/downloads/release/python-346/).
 
 If you install an older version of Python, the installation screen may look a bit different than shown above. Make sure you scroll down to see "Add python.exe to Path", then click the button on the left and pick "Will be installed on local hard drive":
 
@@ -55,7 +55,7 @@ $ python3 --version
 Python {{ book.py_release }}
 ```
 
-If you have a different version of Python installed, at least 3.4.0 (e.g. {{ book.py_release }}), then you don't have to upgrade. If you don't have Python installed, or if you want a different version, first check what Linux distribution you are using with the following command:
+If you have a different version of Python installed, at least {{ book.py_min_version }} (e.g. {{ book.py_release }}), then you don't have to upgrade. If you don't have Python installed, or if you want a different version, first check what Linux distribution you are using with the following command:
 
 {% filename %}command-line{% endfilename %}
 ```
@@ -112,7 +112,7 @@ Python {{ book.py_release }}
 ```
 The version shown may be different from {{ book.py_release }} -- it should match the version you installed.
 
-**NOTE:** If you're on Windows and you get an error message that `python3` wasn't found, try using `python` (without the `3`) and check if it still might be a version of Python that is 3.4.0 or higher. If that doesn't work either, you may open a new command prompt and try again; this happens if you use a command prompt left open from before the Python installation.
+**NOTE:** If you're on Windows and you get an error message that `python3` wasn't found, try using `python` (without the `3`) and check if it still might be a version of Python that is {{ book.py_min_version }} or higher. If that doesn't work either, you may open a new command prompt and try again; this happens if you use a command prompt left open from before the Python installation.
 
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