Add installing git instructions

BUILD.md

@@ -1,21 +1,44 @@
 # Build instructions
 
 ### Prerequisites:
-- git
+- git (see below to know how to install git)
 - A Unity 2020.3.xx LTS version
 - A Machine running Windows, Linux or MacOS
 
-### Instructions:
+### Installing git:
+#### Windows
+1. Grab the installer from [here](https://git-scm.com/download/win).
+2. Follow the usual installation process.
+3. When you reach the step where it asks about PATH enviornment in the installer, choose "Use Git from the Windows Command Prompt".
+4. Now open CMD/Command Prompt/Windows Terminal to use git.
+
+#### Mac
+1. Open the terminal.
+2. Install brew using
+```
+/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
+```
+3. After it finishes installing, install git using
+```
+sudo brew install git
+```
+
+#### Linux
+1. You already know what to do.
+
+
+### Building Heaven Studio:
 1. Clone the repository to your machine
 ```
 git clone https://github.com/megaminerjenny/HeavenStudio.git
 ```
-2. Open Unity 2020.3.xx LTS
-3. Load the HeavenStudio repository you just cloned to Unity
+2. Open Unity 2020.3.xx LTS.
+3. Load the HeavenStudio repository you just cloned to Unity.
 4. After Unity loads, Build AssetBundles by going to Assets -> Build AssetBundles
 5. After Building AssetBundles is done, build the game itself by going to File -> Build Settings -> Build
 6. And done, you now have built the game for your current platform.
 
+
 ### Platform-specific notes:
 - If you get "empty errors" on Linux, run Unity Hub using the following command and load the Unity project through it. This is a general problem with Unity for some users on some distros such as Arch Linux.
 ```