Add reorganize-string.py & Updated README.md

[Gamez0]

Pull Request Template

Description

Count letters in string. If the count of letter is bigger than (n+1)/2 it's impossible.
Else sort the letters by count and than
place the least common letters at the odd indexes
most common letters at the even indexes.

Put check marks:

Have you made changes in README file ?

• Added problem & solution under correct topic.
• Specified Space & Time complexity.
• Specified difficulty level, tag & Note(if any).

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also note any relevant details for your test configuration.

• Test A
• Test B

Make sure all below guidelines are followed else PR will get Reject:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code so that it is easy to understand
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules