Update CONTRIBUTING.md to reference Discord instead of Gitter

[eswarseeram]

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Description

The CONTRIBUTING.md file currently references "TheAlgorithms room in GITTER" for community questions, but the repository has migrated to Discord for community communication.

Current Text

In the section "Do you have questions about the source code?", it says:

Ask any question about how to use the repository in the TheAlgorithms room in GITTER

Suggested Change

The text should be updated to reference Discord instead, which is shown in the README badges.

Location

File: CONTRIBUTING.md Section: "Do you have questions about the source code?"

This is a small documentation update to keep the contributing guidelines consistent with the current community platform.

Additional information

No response