`-rdynamic` flag is needed to properly export the symbols (otherwise Godot may not find them).
Also changed to use the more common `.o` extension for objects on Linux.
Improve language somewhat, and more details where relevant (e.g.
regarding the version of godot_headers).
Add a section on using the GDNativeLibrary editor plugin.
* Format folder/file names with monospace font
Formatting the folder/file names "as code" (i.e. in a monospace font) is more consistent with the rest of the document formatting, helps the names stand out and hopefully draws attention to the need to manually create the subfolders.
* Format another filename as monospace
* Format .gdignore filename as monospaced