Update README.md

Author: varun-r-mallya

README.md

@@ -6,19 +6,63 @@
 
 This is an LLVM IR generator for eBPF programs in Python. We use llvmlite to generate LLVM IR from pure Python. This is then compiled to LLVM object files, which can be loaded into the kernel for execution. We do not rely on BCC to do our compilation.
 
-#  Installation
+##  Installation
 - Have `clang` installed.
 - `pip install pythonbpf`
 
+## Usage
+```python
+# pythonbpf_example.py
+import pythonbpf as pb
+from pythonbpf.helpers import bpf_ktime_get_ns
+from pythonbpf.maps import HashMap
+
+from ctypes import c_void_p, c_int64, c_int32, c_uint64
+
+@pb.bpf
+@pb.map
+def last() -> HashMap:
+    return HashMap(key_type=c_uint64, value_type=c_uint64, max_entries=1)
+
+@pb.bpf
+@pb.section("tracepoint/syscalls/sys_enter_execve")
+def hello(ctx: c_void_p) -> c_int32:
+    print("entered")
+    return c_int32(0)
+
+@pb.bpf
+@pb.section("tracepoint/syscalls/sys_exit_execve")
+def hello_again(ctx: c_void_p) -> c_int64:
+    print("exited")
+    key = 0
+    tsp = last().lookup(key)
+    print(tsp)
+    ts = bpf_ktime_get_ns()
+    return c_int64(0)
+
+@pb.bpf
+@pb.bpfglobal
+def LICENSE() -> str:
+    return "GPL"
+
+def some_normal_function():
+    print("normal function")
+
+# compiles and dumps object file in the same directory
+pb.compile()
+```
+- Run `python pythonbpf_example.py` to get the compiled object file that can be then loaded into the kernel.
+
 ## Development
-Step 0. Make a virtual environment and activate it using `python3 -m venv .venv && source .venv/bin/activate`.  
-Step 1. Run `make install` to install the required dependencies.  
-Step 2. Run `make` to see the compilation output of the example.  
-Step 3. Run `check.sh` to check if generated object file passes through the verifier inside the examples directory.  
-Step 4. Run `make` in the `examples/c-form` directory to modify the example C BPF program to check the actual LLVM IR generated by clang.  
+- Make a virtual environment and activate it using `python3 -m venv .venv && source .venv/bin/activate`.  
+- Run `make install` to install the required dependencies.  
+- Run `make` to see the compilation output of the example.  
+- Run `check.sh` to check if generated object file passes through the verifier inside the examples directory.  
+- Run `make` in the `examples/c-form` directory to modify the example C BPF program to check the actual LLVM IR generated by clang.
 
 ### Development Notes
-Run ` ./check.sh run execve2.o;` in examples folder
+- Run ` ./check.sh check execve2.o;` in examples folder to check if the object code passes the verifier.
+- Run ` ./check.sh run execve2.o;` in examples folder to run the object code using `bpftool`.
 
 ## Authors
 - [@r41k0u](https://github.com/r41k0u)