Documenting config file size limits [Issue #63 - Document NGINX config file limits]

[DeeptiN1]

Proposed changes

Problem: Document NGINX config file limits (#63)

Solution:
Added config file size limits on the Add a file to an instance page.

Testing: Tested on local machine on running the Hugo server locally. Screenshot of change:

Please focus on (optional): Proposed solution on Issue#63 was to add the config file size limits on the Add an NGINX instance page.
However, the Add a file to an instance page seems like a better place to add this information. @mjang Please could you review this and suggest changes?

If this PR addresses an issue on GitHub, ensure that you link to it here:

Closes Issue#63

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[DeeptiN1]

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