modules stuff added

markdown-version/modules.md

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+# Modules
+Python modules allows us to reuse our own code or sometimes use somebody else's code.
+We can write our own modules or we can use modules written by someone else like `requests`,`datetime` and `etc`.
+
+**Note**: It's just a `python` file.
+
+## Built-in Modules
+There built-in python modules that come by default.
+List can be found here [LIST OF MODULES](https://docs.python.org/3/py-modindex.html)
+
+- We can import modules by using `import` keyword
+- We can also give modules an `alias` when we have long module names like `import random as r`.
+- We can also import few functions from the modules `from random import randint`.
+- If you want to import everything from random we do something like this `from random import *`
+
+## Custom Modules
+Custom module is just file with python code.