Add comment documenting why 'attach' is re-spelled to 'attatch'

[DanVanAtta]

1.8 maps and previous named attachment as 'attatchment'

Testing

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Additional Notes to Reviewer

Release Note

[codecov]

Codecov Report

Merging #7661 into master will increase coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #7661   +/-   ##
=========================================
  Coverage     24.43%   24.43%           
- Complexity     7150     7152    +2     
=========================================
  Files          1218     1218           
  Lines         79070    79070           
  Branches      11325    11325           
=========================================
+ Hits          19318    19320    +2     
+ Misses        57576    57575    -1     
+ Partials       2176     2175    -1     

Impacted Files	Coverage Δ	Complexity Δ
...s/strategy/engine/data/ChangeAttachmentChange.java	74.28% <ø> (ø)	5.00 <0.00> (ø)
.../games/strategy/engine/data/DefaultAttachment.java	95.74% <ø> (ø)	26.00 <0.00> (ø)
...va/games/strategy/engine/data/NamedAttachable.java	100.00% <ø> (ø)	5.00 <0.00> (ø)
...trategy/triplea/attachments/TriggerAttachment.java	61.25% <ø> (ø)	261.00 <0.00> (ø)
.../java/games/strategy/triplea/delegate/Matches.java	43.69% <0.00%> (+0.10%)	361.00% <0.00%> (+1.00%)
.../src/main/java/games/strategy/net/nio/Decoder.java	67.24% <0.00%> (+1.72%)	12.00% <0.00%> (+1.00%)

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