Improve README.md with package instructions and formatting (#1, #4)

README.md

@@ -1,27 +1,61 @@
 # VFDecrypt
 
-[VFDecrypt](https://www.theiphonewiki.com/wiki/VFDecrypt) is used to decrypt Apple iOS root filesystem images. Root filesystem images inside IPSW files are encrypted for iOS >= 9. Since iOS 10, root filesystem images are not encrypted and VFDecrypt is no longer required.
+[VFDecrypt](https://www.theiphonewiki.com/wiki/VFDecrypt) is used to decrypt Apple iOS root filesystem images.
+Root filesystem images inside IPSW files are encrypted for iOS >= 9.
+Since iOS 10, root filesystem images are not encrypted and VFDecrypt is no longer required.
 
-Decrypting root filesystem images requires the decryption key. This is provided for most root filesystem images version by the community at [The iPhone Wiki](https://www.theiphonewiki.com/wiki/Firmware_Keys).
+Decrypting root filesystem images requires the decryption key.
+This is provided for most root filesystem images version by the community at [The iPhone Wiki](https://www.theiphonewiki.com/wiki/Firmware_Keys).
 
-There are several VFDecrypt builds available on the Internet. We've used and updated the implementation [here](https://github.com/trailofbits/iverify-oss/tree/master/vendor/vfdecrypt). We've updated `vfdecrypt.c` to support OpenSSL >= 1.1.0 and the `Makefile` to be OS-dependent.
+There are several VFDecrypt builds available on the internet.
+We've used and updated the implementation [here](https://github.com/trailofbits/iverify-oss/tree/master/vendor/vfdecrypt).
+We've updated `vfdecrypt.c` to support OpenSSL >= 1.1.0 and the `Makefile` to be OS-dependent.
 
-You build `vfdecrypt` using
+### Dependencies
+
+To build and run vfdecrypt locally, you need to install the following dependencies:
+
+* macOS
 
+```console
+brew install openssl make
 ```
-make
+
+* Ubuntu/Debian
+
+```console
+sudo apt-get update
+sudo apt-get install -y build-essential libssl-dev coreutils
+```
+
+* Fedora/RHEL/CentOS
+
+```console
+sudo dnf install -y gcc gcc-c++ make openssl-devel coreutils
 ```
 
-You runn `vfdecrypt` by passing it the root filesystem key, the root filesystem image and the output (decrypted) file:
+* Arch Linux
 
+```console
+sudo pacman -S base-devel openssl coreutils
 ```
+
+You build `vfdecrypt` using
+
+```console
+make
+```
+
+You run `vfdecrypt` by passing it the root filesystem key, the root filesystem image and the output (decrypted) file:
+
+```console
 ./vfdecrypt -i ~/Projects/store/out/iPhone5,1_9.3_13E237/058-25512-331.dmg -k 2a66fd6377af8f60d5e300ac3aa8d9c44a1c0dee94579ad3f8a26515debbf381bb971ae8 -o decrypted.dmg
 ```
 
 iExtractor runs `vfdecrypt` as part of the `bin/decrypt_fs` and `scripts/decrypt_fs` scripts.
 
 The usage inside iExtractor:
 
-```
+```console
 docker run -v "<input_absolute_path>":/in -v "<output_absolute_path>":/out -t ghcr.io/malus-security/vfdecrypt:latest -k<rootfs_key> /in /out > /dev/null 2>&1
 ```