message: Add a note for `--msvs_version` to the Windows build.
  #codehealth
diff: @@ -22,7 +22,7 @@ python3 -m pip install six
  "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsamd64_x86.bat"
  cd C:\work\mozc\src
  -python build_mozc.py gyp --qtdir=C:\Qt\Qt5.15.2\msvc2019
  +python build_mozc.py gyp --qtdir=C:\Qt\Qt5.15.2\msvc2019 --msvs_version=2019
  python build_mozc.py build -c Release package
  ```
  @@ -94,11 +94,17 @@ To build Mozc with GUI tools, you need to specify the Qt directory.
  ```
  cd C:\work\mozc\src
  -python build_mozc.py gyp --qtdir=C:\Qt\Qt5.15.2\msvc2019
  +python build_mozc.py gyp --qtdir=C:\Qt\Qt5.15.2\msvc2019 --msvs_version=2019
  python build_mozc.py build -c Release package
  ```
  -The directory of Qt (`C:\Qt\Qt5.12.2\msvc2019` in this example) differs based on Qt version. If you specify `--noqt` option instead of `--qtdir=<dir to Qt>`, mozc\_tool will be built as a mock version, which does nothing.
  +The directory of Qt (`C:\Qt\Qt5.12.2\msvc2019` in this example) differs
  +based on Qt version. If you specify `--noqt` option
  +instead of `--qtdir=<dir to Qt>`, mozc\_tool will be built as a mock version,
  +which does nothing.
  +
  +You need to specify your Visual Studio version to `--msvs_version`.
  +The default value is `2017`.
  If you need debug information, you can build debug version of Mozc as follows.
  