Fix README instructions for launching with Docker

[coveralls]

Pull Request Test Coverage Report for Build 1159

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 32 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.4%) to 72.825%

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Files with Coverage Reduction	New Missed Lines	%
conpot/protocols/http/command_responder.py	1	62.55%
conpot/protocols/ftp/ftp_handler.py	14	79.44%
conpot/protocols/ftp/ftp_base_handler.py	17	80.12%
<!--	Total:	32		-->

Totals
Change from base Build 1158:	0.4%
Covered Lines:	5515
Relevant Lines:	7573

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💛 - Coveralls

[glaslos]

This was made obsolete by #498