Improve CLI documentation for pack build --tag

[importhuman]

Closes #1136

Signed-off-by: Ujjwal Goyal importujjwal@gmail.com

Summary

Adds a line describing the format of tags to be supplied to pack build image --tag

Documentation

• Should this change be documented?
  • Yes
  • No

Related

Resolves #1136

[codecov]

Codecov Report

Merging #1266 (ee17dc4) into main (c81d8bd) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1266   +/-   ##
=======================================
  Coverage   81.19%   81.19%           
=======================================
  Files         140      140           
  Lines        8596     8596           
=======================================
  Hits         6979     6979           
  Misses       1180     1180           
  Partials      437      437           

Flag	Coverage Δ
os_linux	79.83% <100.00%> (+0.07%)	⬆️
os_macos	77.08% <100.00%> (ø)
os_windows	81.09% <100.00%> (ø)
unit	81.19% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[aemengo]

To be honest, I'm a slightly, slightly conflicted by this. Although the help message is correct, it implies that pack is treating a "tag" differently than other tools in the ecosystem. And it's not.

[importhuman]

@aemengo not sure I understand, can you please elaborate? 😅 Any changes you'd suggest?

[jromero]

To be honest, I'm a slightly, slightly conflicted by this. Although the help message is correct, it implies that pack is treating a "tag" differently than other tools in the ecosystem. And it's not.

@aemengo, I see where you are coming from. This isn't the first time this confusion has come up. I've opened a discussion for this topic. buildpacks/community#128 (comment)

At this point, I'd like to consider keeping that discussion out of this PR and focus on the clarification it's provided for how the implementation currently exists.

[jromero]

Accepting as-is for now but heavily considering a change to it's implementation to support "true" tags are defined by the OCI spec. See buildpacks/community#128 (comment)