doc: some info about Travis.

doc/platforms-ios.dox

@@ -34,7 +34,8 @@ namespace Magnum {
 With Apple decision to focus on Metal, iOS OpenGL ES support is stuck on
 version 3.0 (i.e., a version before compute shaders are available).
 
-See also @ref Platform::Sdl2Application for more information.
+See also @ref Platform::Sdl2Application for more information. Some of the
+@ref platforms-macos "macOS platform-specific info" applies here as well.
 
 @section platforms-ios-best-practices Best practices
 

doc/platforms-linux.dox

@@ -32,8 +32,64 @@ namespace Magnum {
 @m_footernavigation
 
 @todoc packages
+@todoc code coverage
 @todoc desktop ES
+@todoc archlinux PKGBUILDs
 @todoc tests, mesa softpipe
+
+@section platforms-linux-travis Setting up Linux build on Travis CI
+
+In general, a Linux build is done by adding the following to your `.travis.yml`
+matrix build. Currently Ubuntu 14.04 is the latest you can get. See
+[the official documentation](https://docs.travis-ci.com/user/reference/trusty/)
+for more information.
+
+@code{.yml}
+matrix:
+  include:
+  - language: cpp
+    os: linux
+    dist: trusty
+    compiler: gcc
+@endcode
+
+It's advisable to use the container builds instead of the sudo-enabled ones as
+they are generally much faster to boot up, however they have restrictions on
+what packages can be installed. Installing packages is done by adding the
+following to your `.travis.yml`
+
+@code{.yml}
+matrix:
+  include:
+  - language: cpp
+    os: linux
+    ...
+    addons:
+      apt:
+        packages:
+        - ninja-build
+        - libsdl2-dev
+        ...
+@endcode
+
+You can find out how's the package named by searching for Ubuntu Trusty
+packages. The packages are whitelisted, be sure to check the `ubuntu-trusty`
+file in https://github.com/travis-ci/apt-package-whitelist before adding a
+package to the list. Some packages might require enabling a third-party PPA, a
+whitelist for them is at https://github.com/travis-ci/apt-source-whitelist. If
+a package is not whitelisted, you can either request it by opening an issue on
+these repos (prepare that it may take *long* to get through in some cases), or
+build it manually and then cache the result.
+
+Travis supports ANSI color escape codes, so don't forget to enable colored
+output for @ref Corrade::TestSuite output. It supports more than just ANSI
+color escaping --- if you use Ninja, it will display just the condensed
+single-line output.
+
+@code{.sh}
+CORRADE_TEST_COLOR=ON ctest -V
+@endcode
+
 */
 
 }

doc/platforms-macos.dox

@@ -32,7 +32,7 @@ namespace Magnum {
 @m_footernavigation
 
 @todoc homebrew
-@todoc travis setup
+@todoc code coverage
 @todoc bundling, dmg cpack
 
 With Apple decision to focus on Metal, macOS OpenGL support is stuck on version
@@ -45,6 +45,35 @@ Official Apple documentation:
 -   [Best Practices for Working with Vertex Data](https://developer.apple.com/library/mac/#documentation/graphicsimaging/Conceptual/OpenGL-MacProgGuide/opengl_vertexdata/opengl_vertexdata.html)
 -   [Best Practices for Working with Texture Data](https://developer.apple.com/library/mac/#documentation/graphicsimaging/Conceptual/OpenGL-MacProgGuide/opengl_texturedata/opengl_texturedata.html)
 
+@section platforms-macos-travis Setting up macOS build on Travis CI
+
+A lot of Travis features is shared between Linux and macOS, see
+@ref platforms-linux-travis for more information.
+
+In general, a macOS build is done by adding the following to your `.travis.yml`
+matrix build. See [the official documentation](https://docs.travis-ci.com/user/reference/osx/)
+for more information.
+
+@code{.yml}
+matrix:
+  include:
+  - language: cpp
+    os: osx
+    compiler: clang
+@endcode
+
+Most of the build setup can be shared with Linux, as both systems have roughly
+the same set of packages. For installing dependencies there's no builtin way,
+but you can use Homebrew. Be aware that calling for example
+@cb{.sh} brew install ninja @ce by default causes Homebrew to update itself
+first. That currently (March 2018) takes almost two minutes. It's possible to
+skip the update by setting an environment variable as shown below, however this
+might fail in case you need a very recent version of a package.
+
+@code{.sh}
+HOMEBREW_NO_AUTO_UPDATE=1 brew install ninja
+@endcode
+
 @section platforms-macos-troubleshooting Troubleshooting
 
 -   @ref AbstractShaderProgram::validate() expects that the shader has a