docs: add documentation for oras completion

docs/commands/oras_completion.mdx

@@ -0,0 +1,33 @@
+---
+title: oras completion
+sidebar_position: 45
+---
+
+# oras completion
+
+`oras completion` helps to generate the autocompletion script for oras for the specified shell.
+
+Based on the shell that you use (bash/fish/powershell/zsh), please run:
+
+```
+oras completion [shell] --help
+```
+
+This will return an output on how you can set up `oras completion` for your shell.
+
+For example, the following steps are to be followed to set it up for `zsh` on macOS:
+
+```
+$ echo "autoload -U compinit; compinit" >> ~/.zshrc
+$ source <(oras completion zsh); compdef _oras oras
+$ oras completion zsh > $(brew --prefix)/share/zsh/site-functions/_oras
+```
+
+After setting it up, you can hit `tab` to autocomplete your commands.
+
+## Options
+
+```
+  -h, --help                                            help for [shell]
+      --no-descriptions                                 disable completion descriptions
+```