Add HTTP support and update checking

docs/compiling.md

@@ -6,24 +6,31 @@ The following tools are required for all platforms:
 - CMake >= 3.12
 - Flex (>= 2.6.4) and Bison (>= 3.5.1)
 - A C++11 compiler
-- OpenAL SDK (can be found [here](https://github.com/kcat/openal-soft))
+- [SDL2](https://github.com/libsdl-org/SDL/tree/SDL2)
+- [OpenAL SDK](https://github.com/kcat/openal-soft)
+
+The following tools may be useful:
+- [OpenSSL](https://github.com/openssl/openssl)
 
 The installation directory can be set to the MOHAA directory with `-DCMAKE_INSTALL_PREFIX=/path/to/mohaa`.
 
 Compiling debug binaries will result in a `-dbg` suffix appended to the name of the binaries to avoid mixing debug/release code.
 
+OpenSSL is used to access websites using TLS over HTTP. It is currently used to check for a new release. If OpenSSL is not installed, OpenMoHAA will be unable to check for new updates automatically.
+
 ## Compiling for Linux
 
 These are the tools required on Linux :
 - Clang >= 7.0.1 or GCC >= 9.4.0
 - libsdl2-dev
 - libopenal-dev
+- libssl-dev
 
 **clang-7** and **gcc-9** has been tested to work on Ubuntu 20.04. Although it's best to use the latest versions.
 
 1 line install command with clang:
 ```sh
-sudo apt-get install -y cmake ninja-build clang lld flex bison libsdl2-dev libopenal-dev
+sudo apt-get install -y cmake ninja-build clang lld flex bison libsdl2-dev libopenal-dev libssl-dev
 ```
 
 Example with **CMake** and **ninja-build** installed:
@@ -43,6 +50,8 @@ OpenAL can be downloaded from here: https://github.com/kcat/openal-soft/releases
 
 Append `-DFLEX_EXECUTABLE=...\win_flex.exe -DBISON_EXECUTABLE=...\win_bison.exe -DOPENAL_INCLUDE_DIR="path/to/oal/include" -DOPENAL_LIBRARY="path/to/oal"` to the CMake command-line to use the package from the link above.
 
+Optionally, you can append `-DOPENSSL_ROOT_DIR=path\to\openssl\install` to specify the path to OpenSSL.
+
 ## Tweaking the build
 
 - `-DBUILD_NO_CLIENT=1` Don't build client binaries. This will only build the dedicated server binaries.