Add vcpkg installation instructions

[FrankXie05]

bde is available as a port in vcpkg, a C++ library manager that simplifies installation for bde and other project dependencies. Documenting the install process here will help users get started by providing a single set of commands to build bde, ready to be included in their projects.

We also test whether our library ports build in various configurations (dynamic, static) on various platforms (OSX, Linux, Windows: x86, x64) to keep a wide coverage for users.

I'm a maintainer for vcpkg, and here is what the port script looks like. We try to keep the library maintained as close as possible to the original library.😊

[osubboo]

1. Those instructions do not work (tried from powershell & git bash):
   .\vcpkg.exe install bde
   Computing installation plan...
   A suitable version of cmake was not found (required v3.24.0). Downloading portable cmake v3.24.0...
   Downloading cmake...
   https://github.com/Kitware/CMake/releases/download/v3.24.0/cmake-3.24.0-windows-i386.zip -> C:\Users\osubbotin\work\vcpkg\vcpkg\downloads\cmake-3.24.0-windows-i386.zip
   Extracting cmake...
   bde[core]:x86-windows is only supported on '!windows & !arm'

2. Port script uses waf build system that is not supported for a few years now.
   This probably means that this port uses very old BDE code base (3.2.0 as I see; waf does not work with the current version of bde (3.107.0)).

[FrankXie05]

Currently, vcpkg supports bde version 4.14.0.

https://github.com/microsoft/vcpkg/blob/3de032f834a9b28a455e35600b03e9d365ce3b85/ports/bde/vcpkg.json#L4

PS G:\bud\vcpkg> ./vcpkg install bde
Computing installation plan...
The following packages will be built and installed:
    bde:x64-windows@4.14.0.0
Detecting compiler hash for triplet x64-windows...
Compiler found: C:/Program Files/Microsoft Visual Studio/2022/Community/VC/Tools/MSVC/14.39.33519/bin/Hostx64/x64/cl.exeRestored 0 package(s) from F:\VCPKG_CACHE in 7.11 ms. Use --debug to see more details.
Installing 1/1 bde:x64-windows@4.14.0.0...
Building bde:x64-windows@4.14.0.0...
-- Note: bde only supports static library linkage. Building static library.
Downloading bloomberg-bde-tools-4.13.0.0.tar.gz
Successfully downloaded bloomberg-bde-tools-4.13.0.0.tar.gz.
-- Extracting source G:/bud/vcpkg/downloads/bloomberg-bde-tools-4.13.0.0.tar.gz
-- Using source at G:/bud/vcpkg/buildtrees/bde/src/4.13.0.0-64d054b347.clean
-- Configure bde-tools-v
Downloading bloomberg-bde-4.14.0.0.tar.gz
Successfully downloaded bloomberg-bde-4.14.0.0.tar.gz.
-- Extracting source G:/bud/vcpkg/downloads/bloomberg-bde-4.14.0.0.tar.gz
-- Using source at G:/bud/vcpkg/buildtrees/bde/src/4.14.0.0-15aa00dc79.clean
-- Configuring x64-windows
CMake Warning at installed/x64-windows/share/vcpkg-cmake/vcpkg_cmake_configure.cmake:344 (message):
  The following variables are not used in CMakeLists.txt:

      BDE_BUILD_TARGET_DBG

  Please recheck them and remove the unnecessary options from the
  `vcpkg_cmake_configure` call.

  If these options should still be passed for whatever reason, please use the
  `MAYBE_UNUSED_VARIABLES` argument.
Call Stack (most recent call first):
  ports/bde/portfile.cmake:30 (vcpkg_cmake_configure)
  scripts/ports.cmake:196 (include)


-- Building x64-windows-dbg
-- Building x64-windows-rel
-- Building x64-windows-dbg
-- Building x64-windows-rel
CMake Warning (dev) at downloads/tools/cmake-3.30.1-windows/cmake-3.30.1-windows-i386/share/cmake-3.30/Modules/GNUInstallDirs.cmake:253 (message):
  Unable to determine default CMAKE_INSTALL_LIBDIR directory because no
  target architecture is known.  Please enable at least one language before
  including GNUInstallDirs.
Call Stack (most recent call first):
  ports/bde/portfile.cmake:52 (include)
  scripts/ports.cmake:196 (include)
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Installing: G:/bud/vcpkg/packages/bde_x64-windows/share/bde/copyright
-- Using cached msys2-mingw-w64-x86_64-pkgconf-1~2.3.0-1-any.pkg.tar.zst
-- Using cached msys2-msys2-runtime-3.5.4-2-x86_64.pkg.tar.zst
-- Using msys root at G:/bud/vcpkg/downloads/tools/msys2/21caed2f81ec917b
-- Performing post-build validation
Stored binaries in 1 destinations in 25 s.
Elapsed time to handle bde:x64-windows: 5.5 min
bde:x64-windows package ABI: 7850f364f5a15a5e55988e3288c175b962096102a0bd67af4c8a6f2128fdc5ac
Total install time: 5.5 min
bde provides CMake targets:

  # this is heuristically generated, and may not be correct
  find_package(bal CONFIG REQUIRED)
  # note: 7 additional targets are not displayed.
  target_link_libraries(main PRIVATE bal balb-iface ball-iface balm-iface)

  find_package(bdl CONFIG REQUIRED)
  # note: 16 additional targets are not displayed.
  target_link_libraries(main PRIVATE bdl bdlb-iface bdlc-iface bdld-iface)

  find_package(bsl CONFIG REQUIRED)
  # note: 13 additional targets are not displayed.
  target_link_libraries(main PRIVATE bsl bsla-iface bslh-iface bsls-iface)

  find_package(inteldfp CONFIG REQUIRED)
  target_link_libraries(main PRIVATE inteldfp)

  find_package(pcre2 CONFIG REQUIRED)
  target_link_libraries(main PRIVATE pcre2)

  find_package(ryu CONFIG REQUIRED)
  target_link_libraries(main PRIVATE ryu)

  find_package(s_baltst CONFIG REQUIRED)
  target_link_libraries(main PRIVATE s_baltst)

PS G:\bud\vcpkg>