chore: add .cargo and assets for rustdoc build

.cargo/config.toml

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+[build]
+rustdocflags = ["--html-in-header", "assets/header.html", "--default-theme", "light", "--extend-css","assets/doc.css"]

assets/doc.css

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+.logo-container img {
+  width: 100% !important;
+}

assets/howto.md

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+
+## How to used
+
+**cargo run --** can be replaced for generated binaries with
+ 
+- target/debug/be-technical-interview-rust (for debug build)
+- target/release/be-technical-interview-rust (for release build)
+
+### For help
+
+```bash
+cargo run -- -h
+```
+
+### For input file **input.txt**
+
+```bash
+cargo run -- -i input.txt
+```
+
+### In quiet mode
+
+```bash
+cargo run -- -i input.txt -q
+```
+
+if **output path** is provided, results will be saved in provided path,<br>
+without **quiet mode** info is printed to terminal
+
+```bash
+cargo run -- -i input.txt -o /tmp/output.txt
+```
+
+### Use config path. **Batch processing in parallel** (one thread for each target) 
+
+```bash
+cargo run -- -c config.toml
+```
+
+### Config file content
+
+```toml
+be_quiet = false
+[[targets]]
+input = "input.txt"
+
+[[targets]]
+input = "input_2.txt"
+```
+
+If **output** path is provided, **out_overwrite** can be used (true or false) to append conten or rewrite.
+
+By default:
+
+- **out_overwrite** is **true**
+- *reg_exp** is set as
+
+```rust
+pub const DEFAULT_REG_EXP: &str = r"(\d+) (\w+) (\d+)";
+```
+
+**reg_exp** can be provided but as a **regex** expresion from **string**, if it can not be converted parser exit.
+
+#### CAUTION
+
+Command line options have precedence over **config path** settings. <br>
+Be careful with the combinations