Updated README.md to include build instructions

Updated Doorstop submodule

README.md

@@ -18,7 +18,17 @@ To disable this console window, pass `--no-console` to the game.
 
 1. Drag & drop the game exe onto **IPA.exe** while holding <kbd>Alt</kbd>
     - Or run `ipa -rn` in a command window
-2. Done
+
+## Arguments
+
+`IPA.exe file-to-patch [arguments]` 
+
+- `--launch`: Launch the game after patching
+- `--revert`: Revert changes made by IPA (= unpatch the game)
+- `--nowait`: Never keep the console open
+- See `-h` or `--help` for more options.
+
+Unconsumed arguments will be passed on to the game in case of `--launch`.
 
 ## How To Develop
 
@@ -33,13 +43,23 @@ See [Developing](https://github.com/nike4613/BeatSaber-IPA-Reloaded/wiki/Develop
 
 BSIPA will automatically repatch the game when it updates, as long as `winhttp.dll` is present in the install directory.
 
-## Arguments
+## Building
 
-`IPA.exe file-to-patch [arguments]` 
+### Prerequisites 
 
-- `--launch`: Launch the game after patching
-- `--revert`: Revert changes made by IPA (= unpatch the game)
-- `--nowait`: Never keep the console open
-- See `-h` or `--help` for more options.
+- Microsoft Visual Studio 2017 or later
+- Tools for C/C++ (MSVC)
+- .NET 4.6 SDK and .NET 4.7.1 SDK
 
-Unconsumed arguments will be passed on to the game in case of `--launch`.
+### Building
+
+1. Clone with `git clone https://github.com/nike4613/BeatSaber-IPA-Reloaded.git --recursive`
+2. Create a file, `bsinstalldir.txt` in the solution root. Do NOT create this in Visual Studio; VS adds a BOM at the begginning of the file that the tools used cannot read. It should contain the path to your Beat Saber installation, using forward slashes with a trailing slash. e.g. 
+```
+C:/Program Files (x86)/Steam/steamapps/common/Beat Saber/
+```
+3. Open `BSIPA.sln` in Visual Studio.
+4. Choose the configuration `x64`
+5. Rebuild all. Any time you make a change, ALWAYS Rebuild All.
+
+When building a Debug build, all referenced assemblies from Beat Saber will be copied from the install directory provided in `bsinstalldir.txt` into `Refs/`. Any new references should reference the copy in there. When building for Release, it just uses the files already in `Refs/`