Update README and FAQ for the new Windows releases

Document how to generate a Windows release from Linux.

It solves the "no output" issue on Windows, so update the FAQ.

FAQ.md

@@ -7,29 +7,8 @@ with it.
 
 Here are the common reported problems and their status.
 
-### On Windows, I have no output in the console
 
-When run in `cmd.exe`, the application does not print anything. Even `scrcpy
+### On Windows, my device is not detected
---help` have no output. We don't know why yet.
-
-However, if you run the very same `scrcpy.exe` from
-[MSYS2](https://www.msys2.org/) (`mingw64`), then it correctly prints output.
-
-As a workaround, redirect outputs to files, so that you can read the files
-afterwards:
-
-```bash
-scrcpy >stdout 2>stderr
-type stdout
-type stderr
-```
-
-_Note that all SDL logs are printed to stderr._
-
-
-### On Windows, when I start the application, nothing happens
-
-The previous problem does not help to get a clue about the cause.
 
 The most common is your device not being detected by `adb`, or is unauthorized.
 Check everything is ok by calling:

README.md

@@ -91,8 +91,37 @@ For Windows, for simplicity, a prebuilt archive with all the dependencies
 
 _(It's just a portable version including _dll_ copied from MSYS2.)_
 
-Instead, you may want to build it manually. You need [MSYS2] to build the
+Instead, you may want to build it manually.
-project. From an MSYS2 terminal, install the required packages:
+
+##### Cross-compile from Linux
+
+This is the preferred method (and the way the release is built).
+
+From _Debian_, install _mingw_:
+
+```bash
+sudo apt install mingw-w64 mingw-w64-tools
+```
+
+You also need the JDK to build the server:
+
+```bash
+sudo apt install openjdk-8-jdk
+```
+
+Then generate the releases:
+
+```bash
+make -f Makefile.CrossWindows
+```
+
+It will generate win32 and win64 releases into `dist/`.
+
+
+##### In MSYS2
+
+From Windows, you need [MSYS2] to build the project. From an MSYS2 terminal,
+install the required packages:
 
 [MSYS2]: http://www.msys2.org/