overlay: change default spdlog level to info

i think users deserve to see a little bit more of useful info,
which also might be actually useful during  troubleshooting.

This is what I get for example:

[MANGOHUD] [error] [cpu.cpp:675] Failed to initialize CPU power data
[MANGOHUD] [info] [gl_renderer.cpp:422] GL version: 4.6
[MANGOHUD] [error] [cpu.cpp:675] Failed to initialize CPU power data
[MANGOHUD] [info] [gpu_fdinfo.h:69] GPU driver is "xe"
[MANGOHUD] [info] [gpu.cpp:69] GPU Found: node_name: renderD128,
vendor_id: 8086 device_id: 56a0 pci_dev: 0000:03:00.0

I don't think that this can be considered too much info.

src/overlay.cpp

@@ -91,7 +91,7 @@ void init_spdlog()
       }
 #ifndef DEBUG
    } else {
-      std::string log_level = "err";
+      std::string log_level = "info";
       transform(log_level.begin(), log_level.end(), log_level.begin(), ::tolower);
       spdlog::set_level(spdlog::level::from_str(log_level));
 #endif