egl/main: Update README.txt

The driver search/load is not done at eglGetDisplay (or eglOpenDisplay
as the readme called it) time, but during eglInitialize().

Drop _eglMain (available only for external drivers) reference. Mention
we use function(s), specific to the built-in driver(s).

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>

src/egl/main/README.txt

@@ -16,10 +16,10 @@ The EGL code here basically consists of two things:
 
 Bootstrapping:
 
-When the apps calls eglOpenDisplay() a device driver is selected and loaded
-(look for dlsym() or LoadLibrary() in egldriver.c).
+When the apps calls eglInitialize() a device driver is selected and loaded
+(look for _eglAddDrivers() and _eglLoadModule() in egldriver.c).
 
-The driver's _eglMain() function is then called.  This driver function
+The built-in driver's entry point function is then called.  This driver function
 allocates, initializes and returns a new _EGLDriver object (usually a
 subclass of that type).
 
@@ -30,10 +30,9 @@ driver->API.Initialize and driver->API.Terminate _must_ be implemented
 with driver-specific code (no default/fallback function is possible).
 
 
-A bit later, the app will call eglInitialize().  This will get routed
-to the driver->API.Initialize() function.  Any additional driver
-initialization that wasn't done in _eglMain() should be done at this
-point.  Typically, this will involve setting up visual configs, etc.
+Shortly after, the driver->API.Initialize() function is executed.  Any additional
+driver initialization that wasn't done in the driver entry point should be
+done at this point.  Typically, this will involve setting up visual configs, etc.