Fix Proposal Stringer

[alexanderbez]

Fix the Stringer interface implementation for the Proposal type:

• Add missing description
• Fix indentation

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• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry: sdkch add [section] [stanza] [message]

• rereviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #3986 into develop will increase coverage by 0.02%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##           develop    #3986      +/-   ##
===========================================
+ Coverage     60.2%   60.23%   +0.02%     
===========================================
  Files          196      196              
  Lines        14551    14554       +3     
===========================================
+ Hits          8761     8767       +6     
+ Misses        5205     5203       -2     
+ Partials       585      584       -1