Update CLI installation instructions for ASDF 0.16

[marckhouzam]

What this PR does / why we need it

ASDF 0.16 has changed their command set.
This PR updates the documentation to match.

Which issue(s) this PR fixes

Fixes # N/A

Describe testing done for PR

# Start from scratch
$ asdf plugin remove tanzu

# Now run the newly documented instructions
$ asdf plugin add tanzu
$ asdf install tanzu latest
Downloading tanzu version 1.5.3
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
100 15.7M  100 15.7M    0     0  9263k      0  0:00:01  0:00:01 --:--:-- 12.1M
Extracting tar for tanzu
x v1.5.3/
x v1.5.3/tanzu-cli-darwin_arm64
Creating bin install directory
Setting /Users/kmarc/.asdf/installs/tanzu/1.5.3/bin/tanzu as executable

$ asdf set --home tanzu latest

$ asdf which tanzu
/Users/kmarc/.asdf/installs/tanzu/1.5.3/bin/tanzu
$ tanzu version
version: v1.5.3
buildDate: 2025-01-29
sha: f73b9ec
arch: arm64

Release note

Update CLI installation instructions for ASDF 0.16

Additional information

Special notes for your reviewer

[anujc25]

LGTM. Thanks