feat: v0.2.0 optimization refactor and docs

- Refactor core traversal to single-pass O(N) tree construction
- Optimize CSV output using `csv` crate for robust escaping
- Optimize JSON output with zero-copy serialization
- Add MANUAL.md
- Bump version to 0.2.0
- Remove walkdir dependency

README.md

@@ -55,9 +55,32 @@ sized /path/to/directory
 sized . -d 1 -i -m 50MB --format csv --save
 ```
 
-**Generate Shell Completions (Zsh):**
+### Generate Shell Completions
+
+**Bash:**
+Add the following to your `.bashrc` or `.bash_profile`:
 ```bash
-sized --completions zsh > _sized
+# Option 1: Source directly
+source <(sized --completions bash)
+
+# Option 2: Save to file (safer startup time)
+sized --completions bash > ~/.sized_completions.bash
+echo "source ~/.sized_completions.bash" >> ~/.bashrc
+```
+
+**Zsh:**
+```bash
+# In your .zshrc
+sized --completions zsh > /usr/local/share/zsh/site-functions/_sized
+# OR
+sized --completions zsh > ~/.zfunc/_sized
+fpath+=~/.zfunc
+autoload -Uz compinit && compinit
+```
+
+**Fish:**
+```bash
+sized --completions fish > ~/.config/fish/completions/sized.fish
 ```
 
 ## License