feat(cli): add version number to cli help string

[justindujardin]

Add the version number to the CLI app's help string so that it's easy to check the installed version:

(.env) √ pathy % pathy
Usage: pathy [OPTIONS] COMMAND [ARGS]...

  Pathy command line interface. (v0.5.1)

Options:
  --install-completion  Install completion for the current shell.
  --show-completion     Show completion for the current shell, to copy it or
                        customize the installation.

  --help                Show this message and exit.

Commands:
  cp  Copy a blob or folder of blobs from one bucket to another.
  ls  List the blobs that exist at a given location.
  mv  Move a blob or folder of blobs from one path to another.
  rm  Remove a blob or folder of blobs from a given location.

[codecov]

Codecov Report

Merging #55 (97fecf4) into master (5bb7e1b) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #55   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines         1027      1028    +1     
=========================================
+ Hits          1027      1028    +1     

Impacted Files	Coverage Δ
pathy/about.py	100.00% <100.00%> (ø)
pathy/cli.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 86a0c3a...97fecf4. Read the comment docs.

[github-actions]

🎉 This PR is included in version 0.5.2 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀