encode64: add README (#7192)

plugins/encode64/README.md

+# encode64
+
+Alias plugin for encoding or decoding using `base64` command
+
+## Functions and Aliases
+
+| Function   | Alias | Description                    |
+| ---------- | ----- | ------------------------------ |
+| `encode64` | `e64` | Encodes given data to base64   |
+| `decode64` | `d64` | Decodes given data from base64 |
+
+## Enabling plugin
+
+1. Edit your `.zshrc` file and add `encode64` to the list of plugins:
+
+   ```sh
+   plugins=(
+     # ...other enabled plugins
+     encode64
+   )
+   ```
+
+2. Restart your terminal session or reload configuration by running:
+
+   ```sh
+   source ~/.zshrc
+   ```
+
+## Usage and examples
+
+### Encoding
+
+- From parameter
+
+  ```console
+  $ encode64 "oh-my-zsh"
+  b2gtbXktenNo
+  $ e64 "oh-my-zsh"
+  b2gtbXktenNo
+  ```
+
+- From piping
+
+  ```console
+  $ echo "oh-my-zsh" | encode64
+  b2gtbXktenNo==
+  $ echo "oh-my-zsh" | e64
+  b2gtbXktenNo==
+  ```
+
+### Decoding
+
+- From parameter
+
+  ```console
+  $ decode64 b2gtbXktenNo
+  oh-my-zsh%
+  $ d64 b2gtbXktenNo
+  oh-my-zsh%
+  ```
+
+- From piping
+
+  ```console
+  $ echo "b2gtbXktenNoCg==" | decode64
+  oh-my-zsh
+  $ echo "b2gtbXktenNoCg==" | decode64
+  oh-my-zsh
+  ```