update Readme

sources/README.md

@@ -1,16 +1,46 @@
 # Tektur sources
 
-The preferred modification format is FontLab 7 `.vfj`.
+The preferred modification format is FontLab 7 `.vfj`. TypeRig is recommended for exporting features.
 The `UFO/*.designspace` files are not as exported from FontLab and should not be overwritten.
 
+
 ## Exporting FontLab sources to UFO
 
 1. Export `DesignSpace+UFO` from FontLab (Destination: Source, Subfolders by: none).
-2. For each master, build `mark/mkmk` features in FontLab and export them using the `exportFeatures.py` script from within FontLab. This is preferred because FontLab cannot export correct `mark/mkmk` for each master on its own and only exports these features as created, duplicating one master’s features in all masters. (Google Fonts is no better and strips mark attachment features from the webfonts altogether, but whatever).
+2. For each master, build `mark/mkmk` features in FontLab and export them from FontLab using the `exportFeatures.py` script (which uses TypeRig). This is preferred because FontLab cannot export correct `mark/mkmk` for each master on its own and only exports these features as created, duplicating one master’s features in all masters.
 3. Move the `masters` directory from `/sources/FontLab/` to `/sources/UFO/`.
 
-## Building the fonts
 
-Make sure you have Python 3 installed. Create a `virtualenv` if you like. Install prerequisites from `/requirements.txt`.
+## Setting up a build environment
+
+A Linux system is recommended. Under Windows, you can use a Linux Subsystem for Windows.
+Make sure you have Python 3 installed.
+
+Create a `virtualenv` if you like:
+
+```bash
+sudo apt-get update
+sudo apt install python3-virtualenv
+```
+
+Get your python location: `which python3`, then use it in the project’s directory to create a `virtualenv`:
+
+```bash
+virtualenv --python=/usr/bin/python3 ./build
+```
+
+Activate the `virtualenv`:
+
+```bash
+source ./build/bin/activate
+```
+
+Install prerequisites from `/requirements.txt`:
+
+```bash
+pip install -r ./requirements.txt
+```
+
+## Building the fonts
 
-1. Open terminal in `/sources`. Run `./build.sh`.
+Open terminal in `/sources`. Run `./build.sh`.