Add Obsidian to Markdown Tools Section

[pehlicd]

Added Obsidian to Markdown Tools section.

Types of Changes

What types of changes does your PR introduce? Put an x in all boxes that apply

• New addition to list
• Fixing bug in existing item in list
• Removing item from list
• Changing structure (organization) of list

Proposed Changes

Added Obsidian end of the markdown tools list.
Obsidian is a great markdown tool which I have been using for months now. It has so much cool features that is why it should be on that list.

PR Checklist

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• I have read the CONTRIBUTING guide
• I have explained why this PR is important
• I have added necessary documentation (if appropriate)

Further Comments

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