Updated Readme file for the slack community migration

[gabriel-bolbotina]

• removed the Slack icon
• updated the link to the mergin maps community

[coveralls]

Coverage Report for CI Build 31572198954

Coverage decreased (-0.02%) to 83.369%

Details

• Coverage decreased (-0.02%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 1 coverage regression across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

1 previously-covered line in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
mergin/client_pull.py	1	82.54%

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Coverage Stats

Relevant Lines:	5676
Covered Lines:	4732
Line Coverage:	83.37%
Coverage Strength:	0.83 hits per line

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💛 - Coveralls