updated FontVal/Freetype usage instructions on README.md
(issue / issue
@@ -649,7 +649,7 @@ pip install --upgrade git+https://github.com/googlefonts/fontbakery.git;
## Microsoft Font Validator
-A prebuilt binary of the Microsoft Font Validator is currently available at the prebuilt/fval directory in this repo. The corresponding source code is available under a free license at https://github.com/Microsoft/Font-Validator. In order to enable this check, you'll need to have the mono runtime installed in your system. You'll also need to have FontValidator.exe available in the system path. One way to achieved would be:
+A prebuilt binary of the Microsoft Font Validator is currently available at the prebuilt/fval directory in this repo. (The corresponding source code is available under a free license at https://github.com/Microsoft/Font-Validator). In order to enable this check, you'll need to have the mono runtime installed in your system. You'll also need to have FontValidator.exe available in the system path. One way to achieved would be:
```
sudo apt-get install mono-runtime libmono-system-windows-forms4.0-cil
@@ -658,6 +658,17 @@ export PATH=$PATH:$FONTBAKERY_GIT_REPO/prebuilt/fval
...where $FONTBAKERY_GIT_REPO should be the name of the directory where you checked out Font Bakery source code. Obviously, you can also use any other alternative way of making FontValidator.exe available in your system path.
+FontValidator includes some hinting instruction validation tests. These rely on a customized version of the Freetype library. In order to enable those, you'll need to use the custom build available in this repo by doing:
+
+```
+export LD_PRELOAD=$FONTBAKERY_GIT_REPO/prebuilt/custom_freetype/libfreetype.so
+```
+
+The corresponding modified freetype source code is available at:
+https://github.com/felipesanches/freetype2
+
+If your vanilla system freetype is used instead, then all FontValidator tests will still be run, except for the hinting validation ones.
+
## Bash completion
Fontbakery comes with a minimal Bash completion script. It can help you to type the subcommands that follow directly after the `fontbakery` command. Bash completion is accessed by hitting the [TAB] key when entering the command.
