Update README.md

[7brokenmirrors]

Output wasn't dumped to host directory, must be /opt/ instead of /root/

compare:

========== Manager Configuration ==========
{
  "aggregator_address": [
    "127.0.0.1",
    33585
  ],
  "data_directory": "/opt/Desktop/",
  "database_name": "/opt/Desktop/crawl-data.sqlite",
  "failure_limit": null,
  "log_directory": "/opt/Desktop/",
  "log_file": "/opt/Desktop/openwpm.log",
  "logger_address": [
    "127.0.0.1",
    34201
  ],
  "num_browsers": 1,
  "output_format": "local",
  "s3_bucket": null,
  "s3_directory": null,
  "screenshot_path": "/opt/Desktop/screenshots",
  "source_dump_path": "/opt/Desktop/sources",
  "testing": false
}

[codecov]

Codecov Report

Merging #776 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #776   +/-   ##
=======================================
  Coverage   40.06%   40.06%           
=======================================
  Files          29       29           
  Lines        3157     3157           
=======================================
  Hits         1265     1265           
  Misses       1892     1892           

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[vringar]

Thank you for this PR. I don't quite understand why this happens but I could reproduce this behaviour