Update buildpack register example

[dfreilich]

Signed-off-by: David Freilich [email protected]

Summary

Output

Before

 $  pack help buildpack register
(experimental) Register a buildpack to a registry

Usage:
  pack buildpack register <image> [flags]

Examples:
pack register my-buildpack

After

$  go run cmd/pack/main.go help buildpack register
Register a buildpack to a registry

Usage:
  pack buildpack register <image> [flags]

Examples:
pack buildpack register my-buildpack

Related

Resolves #1060

[codecov]

Codecov Report

Merging #1061 (47562a6) into main (3d222b6) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1061   +/-   ##
=======================================
  Coverage   80.21%   80.21%           
=======================================
  Files         130      130           
  Lines        7998     7998           
=======================================
  Hits         6415     6415           
  Misses       1163     1163           
  Partials      420      420           

Flag	Coverage Δ
os_linux	79.57% <100.00%> (ø)
os_macos	76.88% <100.00%> (-0.03%)	⬇️
os_windows	80.13% <100.00%> (ø)
unit	79.60% <100.00%> (ø)

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