Warn when running on Windows

[dorschw]

Related Issues

related: XSUP-32254

Description

• Add a warning log when running on Windows machines
• Update README.md

[coveralls]

Pull Request Test Coverage Report for Build 1644d51b-64a6-4898-87c0-71d16e923f97

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 8002 unchanged lines in 290 files lost coverage.
• Overall coverage decreased (-18.5%) to 80.398%

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Files with Coverage Reduction	New Missed Lines	%
demisto_sdk/commands/common/clients/configs.py	1	97.14%
demisto_sdk/commands/common/content/objects/pack_objects/incident_field/incident_field.py	1	65.0%
demisto_sdk/commands/common/content/objects/pack_objects/job/job.py	1	83.33%
demisto_sdk/commands/common/content/objects/pack_objects/lists/lists.py	1	85.71%
demisto_sdk/commands/common/files/errors.py	1	71.43%
demisto_sdk/commands/common/files/text_file.py	1	78.13%
demisto_sdk/commands/common/hook_validations/deprecation.py	1	98.72%
demisto_sdk/commands/common/hook_validations/job.py	1	98.41%
demisto_sdk/commands/common/hook_validations/layout_rule.py	1	88.89%
demisto_sdk/commands/common/hook_validations/lists.py	1	96.55%

Totals
Change from base Build 7520387020:	-18.5%
Covered Lines:	35253
Relevant Lines:	43848

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💛 - Coveralls

[GuyAfik]

nice work, need a change-log here IMO

[tschanfeld]

documentation updated per @dorschw https://docs-cortex.paloaltonetworks.com/r/1/Demisto-SDK-Guide/Install-Demisto-SDK