Include documentation about semver, releases, and changelog policies

[displague]

This text was off-the cuff starter text, based on the maintenance practices in the Terraform project.

Fixes #25

Part of #24

[codecov-commenter]

Codecov Report

Merging #31 (25d1f7a) into main (4aca376) will decrease coverage by 10.57%. The diff coverage is n/a.

@@             Coverage Diff             @@
##             main      #31       +/-   ##
===========================================
- Coverage   71.68%   61.11%   -10.58%     
===========================================
  Files           9        3        -6     
  Lines         565      216      -349     
  Branches      120       24       -96     
===========================================
- Hits          405      132      -273     
+ Misses        103       75       -28     
+ Partials       57        9       -48     

Impacted Files	Coverage Δ
...ctions/equinix/metal/plugins/module_utils/metal.py	45.76% <0.00%> (-29.67%)	:arrow_down:
...ions/equinix/metal/plugins/modules/project_info.py
...tions/equinix/metal/plugins/modules/sshkey_info.py
...ollections/equinix/metal/plugins/modules/device.py
...tions/equinix/metal/plugins/modules/device_info.py
...ollections/equinix/metal/plugins/modules/sshkey.py
...llections/equinix/metal/plugins/modules/project.py

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