attempt at reproducible tarballs (sdist)

contrib/build-linux/sdist/README.md

@@ -0,0 +1,50 @@
+Source tarballs
+===============
+
+✗ _This script does not produce reproducible output (yet!)._
+
+This assumes an Ubuntu (x86_64) host, but it should not be too hard to adapt to another
+similar system. The docker commands should be executed in the project's root
+folder.
+
+1. Install Docker
+
+    ```
+    $ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
+    $ sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
+    $ sudo apt-get update
+    $ sudo apt-get install -y docker-ce
+    ```
+
+2. Build image
+
+    ```
+    $ sudo docker build -t electrum-sdist-builder-img contrib/build-linux/sdist
+    ```
+
+3. Build source tarballs
+
+    It's recommended to build from a fresh clone
+    (but you can skip this if reproducibility is not necessary).
+
+    ```
+    $ FRESH_CLONE=contrib/build-linux/sdist/fresh_clone && \
+        sudo rm -rf $FRESH_CLONE && \
+        mkdir -p $FRESH_CLONE && \
+        cd $FRESH_CLONE  && \
+        git clone https://github.com/spesmilo/electrum.git && \
+        cd electrum
+    ```
+
+    And then build from this directory:
+    ```
+    $ git checkout $REV
+    $ sudo docker run -it \
+        --name electrum-sdist-builder-cont \
+        -v $PWD:/opt/electrum \
+        --rm \
+        --workdir /opt/electrum/contrib/build-linux/sdist \
+        electrum-sdist-builder-img \
+        ./build.sh
+    ```
+4. The generated distributables are in `./dist`.