docs: Fix GLSL compiler link

The doc wasn't update since we moved the glsl compiler to src/compiler/glsl.
I also updated the description of the standalone compiler.

v2:
 - Mention that just-log argument removes headers/separators.
 - Mention that version argument is mandatory.
Since version argument is mandatory, add --version to the command line
example.

Signed-off-by: Elie Tournier <tournier.elie@gmail.com>
Reviewed-by: Alejandro PiƱeiro <apinheiro@igalia.com>
1 file changed