Add reproducible build instructions

BUILDING.md

@@ -10,43 +10,48 @@ Static builds via Docker are done in 3 steps:
 2. Creating a base Docker image
 3. Using the base image to compile a build
 
-### Windows
+### Linux (reproducible)
 
-The docker image for Windows static compiles uses Ubuntu 18.04 and installs [mxe](https://mxe.cc) from [our git](https://git.wownero.com/feather/mxe/src/branch/feather-patch), 
-which comes with: OpenSSL 1.1.1g, Qt 5.15.0 (OpenGL via mesa). For more information, check the Dockerfile: `Dockerfile_windows`.
+The docker image for reproducible Linux static builds uses Ubuntu 16.04 and compiles the required libraries statically 
+so that the resulting Feather binary is static. For more information, check the Dockerfile: `Dockerfile`.
 
 #### 1. Clone
 
 ```bash
-git clone --recursive https://git.wownero.com/feather/feather.git
+git clone --branch master --recursive https://git.wownero.com/feather/feather.git
 cd feather
 ```
 
-#### 2. Base image
+Replace `master` with the desired version tag (e.g. `beta-1`) to build the release binary.
 
-Warning: Building the MXE base image takes up to a hour, so go watch a movie.
+#### 2. Base image
 
 ```bash
-docker build -f Dockerfile_windows --tag feather:win --build-arg THREADS=8 .
+docker build --tag feather:linux --build-arg THREADS=4 .
 ```
 
-Note: You only need to build the base image once.
+Building the base image takes a while. You only need to build the base image once.
 
 #### 3. Build
 
 ```bash
-docker run --rm -it -v /tmp/ccache:/root/.ccache -v /root/feather:/feather -w /feather feather:win /bin/bash -c 'PATH="/mxe/usr/bin/:$PATH" TOR="/mxe/usr/x86_64-w64-mingw32.static/bin/tor.exe" XMRIG="/xmrig/xmrig.exe" make windows-mxe-release -j8'
+docker run --rm -it -v $PWD:/feather --env OPENSSL_ROOT_DIR=/usr/local/openssl/ -w /feather feather:linux sh -c 'TOR="/usr/local/tor/bin/tor" XMRIG="/xmrig/xmrig" make release-static -j4'
 ```
 
-Replace `PATH_TO_FEATHER` with the absolute path to Feather locally. 
+If you're re-running a build make sure to `rm -rf build/` first.
 
-The resulting binary can be found in `build/bin/feather.exe`.
+The resulting binary can be found in `build/bin/feather`.
 
-### Linux
+Hashes for tagged commits should match:
 
-The docker image for Linux static compiles uses Ubuntu 18.04 and compiles the required libraries statically so that 
-the resulting Feather binary is static. It comes with OpenSSL 1.1.1g, Qt 5.15.0 (OpenGL disabled). For more information, 
-check the Dockerfile: `Dockerfile`.
+```
+beta-1: d1a52e3bac1abbae4adda1fc88cb2a7a06fbd61085868421897c6a4f3f4eb091  feather
+```
+
+### Windows
+
+The docker image for Windows static compiles uses Ubuntu 18.04 and installs [mxe](https://mxe.cc) from [our git](https://git.wownero.com/feather/mxe/src/branch/feather-patch), 
+which comes with: OpenSSL 1.1.1g, Qt 5.15.0 (OpenGL via mesa). For more information, check the Dockerfile: `Dockerfile_windows`.
 
 #### 1. Clone
 
@@ -57,10 +62,10 @@ cd feather
 
 #### 2. Base image
 
-Warning: Building the base image takes a while, go prepare some dinner.
+Warning: Building the MXE base image takes up to a hour, so go watch a movie.
 
 ```bash
-docker build --tag feather:linux --build-arg THREADS=8 .
+docker build -f Dockerfile_windows --tag feather:win --build-arg THREADS=8 .
 ```
 
 Note: You only need to build the base image once.
@@ -68,12 +73,12 @@ Note: You only need to build the base image once.
 #### 3. Build
 
 ```bash
-docker run --env OPENSSL_ROOT_DIR=/usr/local/openssl/ --rm -it -v /tmp/ccache:/root/.ccache -v PATH_TO_FEATHER:/feather -w /feather feather:linux sh -c 'TOR="/usr/local/tor/bin/tor" XMRIG="/xmrig/xmrig" make release-static -j8'
+docker run --rm -it -v /tmp/ccache:/root/.ccache -v /root/feather:/feather -w /feather feather:win /bin/bash -c 'PATH="/mxe/usr/bin/:$PATH" TOR="/mxe/usr/x86_64-w64-mingw32.static/bin/tor.exe" XMRIG="/xmrig/xmrig.exe" make windows-mxe-release -j8'
 ```
 
 Replace `PATH_TO_FEATHER` with the absolute path to Feather locally.
 
-The resulting binary can be found in `build/bin/feather`.
+The resulting binary can be found in `build/bin/feather.exe`.
 
 ## macOS