chore: improvements to book on interface (#1593)

Author: yi-sun

book/src/custom-extensions/overview.md

@@ -28,27 +28,40 @@ Our design for the configuration procedure above was inspired by the [EVMMAX pro
 To use these extensions, you must populate an `openvm.toml` in your package root directory (where the `Cargo.toml` file is located).
 We will explain in each extension how to configure the `openvm.toml` file.
 
-The template `openvm.toml` file is as follows:
+A template `openvm.toml` file using the default VM extensions shipping with OpenVM is as follows:
 
 ```toml
 [app_vm_config.rv32i]
+
 [app_vm_config.rv32m]
+range_tuple_checker_sizes = [256, 8192]
+
 [app_vm_config.io]
+
 [app_vm_config.keccak]
+
 [app_vm_config.sha256]
+
 [app_vm_config.native]
+
 [app_vm_config.bigint]
+range_tuple_checker_sizes = [256, 8192]
+
 [app_vm_config.modular]
 supported_modulus = ["<modulus_1>", "<modulus_2>", ...]
+
 [app_vm_config.fp2]
 supported_modulus = ["<modulus_1>", "<modulus_2>", ...]
+
 [app_vm_config.pairing]
 supported_curves = ["Bls12_381", "Bn254"]
+
 [[app_vm_config.ecc.supported_curves]]
 modulus = "<modulus_1>"
 scalar = "<scalar_1>"
 a = "<a_1>"
 b = "<b_1>"
+
 [[app_vm_config.ecc.supported_curves]]
 modulus = "<modulus_2>"
 scalar = "<scalar_2>"

book/src/getting-started/quickstart.md

@@ -70,7 +70,7 @@ OPENVM_FAST_TEST=1 cargo openvm prove app --input "0x010A00000000000000"
 ```
 
 The `--input` field is passed to the program which receives it via the `io::read` function.
-In our `main.rs` we called `read()` to get `n: u64`. The input here is `n = 10u64` _in little endian_. Note that this value must be padded to exactly 8 bytes (64 bits).
+In our `main.rs` we called `read()` to get `n: u64`. The input here is `n = 10u64` _in little endian_. Note that this value must be padded to exactly 8 bytes (64 bits) and is prefixed with `0x01` to indicate that the input is composed of raw bytes.
 
 The serialized proof will be output to `./openvm/app.proof`.
 

book/src/writing-apps/overview.md

@@ -36,13 +36,13 @@ To see how more complex inputs can be converted into a VM-readable format, see t
 
 ## Generating a Proof
 
-Given an app configuration TOML file, you first need to generate a proving and verifying key:
+To generate a proof, you first need to generate a proving and verifying key:
 
 ```bash
 cargo openvm keygen
 ```
 
-After generating the keys, you can generate a proof by running:
+If you are using custom VM extensions, this will depend on the `openvm.toml` file which encodes the VM extension configuration; see the [custom extensions](../custom-extensions/overview.md) docs for more information about `openvm.toml`. After generating the keys, you can generate a proof by running:
 
 ```bash
 cargo openvm prove app --input <path_to_input | hex_string>