Update cost multiplier link in upgrade scenarios docs

[joseph-robertson]

Closes #408.

[github-actions[bot]]

File	Coverage
All files	85%	:white_check_mark:
base.py	90%	:white_check_mark:
eagle.py	77%	:white_check_mark:
exc.py	57%	:white_check_mark:
local.py	70%	:white_check_mark:
postprocessing.py	84%	:white_check_mark:
utils.py	91%	:white_check_mark:
cloud/docker_base.py	0%	:x:
sampler/base.py	79%	:white_check_mark:
sampler/downselect.py	33%	:white_check_mark:
sampler/precomputed.py	93%	:white_check_mark:
sampler/residential_quota.py	61%	:white_check_mark:
test/test_docker.py	33%	:white_check_mark:
test/test_validation.py	97%	:white_check_mark:
workflow_generator/base.py	90%	:white_check_mark:
workflow_generator/commercial.py	53%	:white_check_mark:
workflow_generator/residential_hpxml.py	86%	:white_check_mark:

Minimum allowed coverage is 33%

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