Add Getting Started doc to the book (#1)

docs/src/user_guide/getting_started.md

@@ -1,3 +1,91 @@
 # Getting Started
+Although currently working with the first releases of Leaf, we aim to provide a rather straightforward workflow for the users.
 
-(TBD)
+Please follow the instruction below to try Leaf in your environment.
+
+## Installing Leaf
+
+### Requirements
+- Rust (`rustup`)
+- Python
+
+You can install Leaf using `cargo` and by building the source code.
+
+1. Clone the repository.
+    ```console
+    $ git clone https://github.com/sfu-rsl/leaf.git
+    $ cd leaf
+    ```
+1. Install Leaf's compiler named as `leafc` using
+    ```console
+    $ cargo install --path ./compiler
+    ```
+## Performing Concolic Execution
+As an instrumentation-based dynamic analyzer, Leaf instruments programs such that
+they expose information about their behavior during each execution.
+Therefore, concolic execution is achieved by compiling the target program and
+running the executable.
+
+1. Pick a program you want to do concolic execution for. Some are available in `samples` directory of the source tree.
+    ```rust
+    fn main() {
+        let x: u8 = 10;
+        if x < 5 {
+            println!("Hello, world!");
+        }
+    }
+    ```
+
+1. Mark a variable interest as symbolic.
+    ```rust
+    // samples/hello_world.rs
+
+    use leaf::annotations::*;
+    fn main() {
+        let x: u8 = 10.mark_symbolic();
+        if x < 5 {
+            println!("Hello, world!");
+        }
+    }
+    ```
+
+1. Compile your target program using `leafc` as you would do with `rustc`. (The first compilation takes longer, bear with it!)
+    ```console
+    $ leafc ./hello_world.rs
+    ```
+
+1. Prepare the environment to observe the execution through the standard error
+   by setting `LEAF_LOG` variable. e.g.,
+    ```bash
+    export LEAF_LOG="info"
+    ```
+1. Execute the compiled program.
+    ```console
+    $ ./hello_world 
+    ```
+1. An output similar to the following is expected from the execution.
+    ```log
+    2024-12-10 00:40:55  INFO leafrt Initializing runtime library
+    2024-12-10 00:40:55  INFO leafrt::pri::basic::instance Initializing basic backend
+    2024-12-10 00:40:55  INFO leafrt::backends::basic::outgen Setting up binary output writing to directory: output
+    2024-12-10 00:40:55  INFO leafrt::pri::basic::instance Basic backend initialized
+    2024-12-10 00:40:55  INFO leafrt::backends::basic::sym_vars Added a new symbolic variable: <Var1: u8> = 10u8
+    2024-12-10 00:40:55  INFO leafrt::trace::log Notified about constraint {!(<(<Var1: u8>, 5u8))} at step Def(0:5)[2]
+    2024-12-10 00:40:55  INFO leafrt::outgen Found a solution:
+    {
+        "1": 0u8,
+    }
+    ```
+    The logs include information about the constraints put on the variables marked as symbolic for the path taken in the execution.
+
+1. Given the current default configuration, a folder named `leaf_out` also gets generated
+   which contains alternative values for the symbolic variables that should cause
+   the execution take other paths than the one taken, which we call diverging inputs.
+   ```console
+   $ ls ./leaf_out
+   0.bin
+   ```
+
+-----------
+
+More details about each step is provided in the rest of the book.