Remove slack line in Assamese translation

[nadhamsaipallavi]

🎯 Goal
Replace link to slack in 'Where to go from here' section in Assamese translation of Readme and put a link to code contributions like in English Readme.

💡 Possible solutions
Remove link to slack in Bulgarian translation and put a link to code contributions repo similar to main Readme.
You can find it in https://github.com/firstcontributions/first-contributions/blob/main/docs/translations/README.assamese.md?plain=1

Important

Please only address one issue in a PR.
Let's make it possible for more people to solve issues here.

📋 Steps to solve the problem

Comment below about what you've started working on.
Add, commit, push your changes.
Submit a pull request and add this in comments - 'Addresses #'
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[GAVARA-PRABHAS-RAM]

Hi, I’m working on this issue to replace the Slack link in the Assamese README with the code contributions link.