Add main page to reference.

lib/include/fedipotato.hpp

@@ -113,3 +113,54 @@ private:
 } // namespace FediPotato
 
 #endif  // FEDIPOTATO_HPP
+
+/*!
+ *  @mainpage FediPotato Reference
+ *
+ *  @section using Using the library
+ *
+ *  Include fedipotato.hpp, which then includes all other headers.
+ *
+ *  @code
+ *  #include <FediPotato/fedipotato.hpp>
+ *  @endcode
+ *
+ *  Use it in your CMake project like this:
+ *
+ *  @code
+ *  find_package(FediPotato REQUIRED CONFIG)
+ *  target_link_libraries(MyProject PRIVATE FediPotato::FediPotato)
+ *  @endcode
+ *
+ *  Or compile your code with `g++ $(pkg-config --cflags --libs FediPotato)`.
+ *
+ *  Since we use C++17 features in the headers of this library, your program
+ *  needs to be compiled as C++17 or higher too.
+ *
+ *  @subsection example Example
+ *
+ *  @code
+ *  #include <FediPotato/fedipotato.hpp>
+ *
+ *  int main()
+ *  {
+ *  }
+ *  @endcode
+ *
+ *  @section exceptions Exceptions
+ *
+ *  We throw exceptions. Consult the documentation for the class constructors
+ *  you use for further information.
+ *
+ *  @section thread_safety Thread safety
+ *
+ *  The first time you construct a FIXME,
+ *  [curl_global_init(3)](https://curl.haxx.se/libcurl/c/curl_global_init.html)
+ *  is called. When the last FIXME is
+ *  destroyed, [curl_global_cleanup(3)]
+ *  (https://curl.haxx.se/libcurl/c/curl_global_cleanup.html) is called. Both
+ *  are not thread safe.
+ *
+ *  If you are using libcurl with OpenSSL before 1.1.0, please read
+ *  [libcurl-thread(3)](https://curl.haxx.se/libcurl/c/threadsafe.html).
+ */