Merge pull request #4516 from maxGimeno/Doc-fix_doc_for_brew-maxGimeno

Documentation: Update installation instructions

Documentation/doc/Documentation/Usage.txt

@@ -60,6 +60,12 @@ On most operating systems, package managers offer \cgal and its essential third
 On macOS, we recommend using of <a href="https://brew.sh/">Homebrew</a> in the following way:
 
     brew install cgal
+    brew install cgal-qt5   #(only for GUI)
+
+You should check that cgal and cgal-qt5 are correctly "linked", especially when upgrading from an old version. If not, run the following command:
+
+    brew link cgal
+    brew link cgal-qt5  #(if you installed it)
 
 On Linux distributions such as `Debian`/`Ubuntu`/`Mint`, use `apt-get` in the following way:
 
@@ -148,10 +154,14 @@ The variable `CGAL_DIR` is also generally found when \cgal has been obtained via
 In the rare event that it has not, the variable `CGAL_DIR` should be set manually to:
 
 <ul>
-<li>something like `/usr/local/Cellar/cgal/CGAL-\cgalReleaseNumber/lib/cmake/CGAL`, for Brew.</li>
+<li>something like `/usr/local/opt/cgal/lib/cmake/CGAL`, for Brew.</li>
 <li>something like `/usr/lib/x86_64-linux-gnu/cmake/CGAL`, for Linux distributions.</li>
 </ul>
 
+Note that you can also use `CMAKE_PREFIX_PATH` to point to a directory that contains all dependencies, like so:
+
+    cmake -DCMAKE_PREFIX_PATH=/my/custom/brew/installation/dir -DCMAKE_BUILD_TYPE=Release .
+
 If \cgal has been obtained via other means, `CGAL_DIR` must point to the root directory
 of the \cgal source code (either the root of the unpacked release tarball or the root
 of the Git working directory).
@@ -162,6 +172,13 @@ if no debugging is intended. Users should thus run:
     cd CGAL-\cgalReleaseNumber/examples/Triangulation_2
     cmake -DCGAL_DIR=$HOME/CGAL-\cgalReleaseNumber -DCMAKE_BUILD_TYPE=Release . # we are here using a release tarball
 
+Note that the package Qt on brew is "keg-only", which means it cannot be "linked" with brew.
+You will have to specify the Qt5_DIR by hand to cmake, using something like
+
+    -DQt5_DIR=/usr/local/opt/qt/lib/cmake/Qt5
+
+where '/usr/local/` is actually your current brew installation directory.
+
 \subsection usage_configuring_cmake_gui Specifying Missing Dependencies
 
 The configuration process launched above might fail if CMake fails to find

Documentation/doc/Documentation/windows.txt

@@ -37,8 +37,8 @@ The first step is to clone or download `vcpkg` from
 
 By default `vcpkg` installs for 32 bit binaries and will use the latest version of Visual C++
 installed on your machine.   If you develop 64 bit software you must
-set the Windows environment variable `VCPKG_DEFAULT_TRIPLE` to `x64-windows`
-or pass the option `--triplet x64-windows` whenever you install a package.
+set the Windows environment variable `VCPKG_DEFAULT_TRIPLET` to `x64-windows`
+or add the suffix `:x64-windows` to the package name you want to install (for example `cgal:x64-windows`).
 We refer to the
 <a href="https://github.com/microsoft/vcpkg/blob/master/docs/examples/installing-and-using-packages.md#step-2-use">official documentation</a>
 of `vcpkg` if you want to compile for an older version of a compiler.