docs: Clarify string encoding for GFile constructors
docs: Clarify string encoding for GFile constructors

The encoding was deduced from looking at the source code, feel free to
fix if it's wrong (the docs _and_ the source code).

Distrotech/glib,bluez-android/glib,pstglia/platform-external-bluetooth-glib,lukasz-skalski/glib,justinkb/aosp-bluez.glib,Distrotech/glib,djdeath/glib,ieei/glib,djdeath/glib,dicer/android_external_glib,iConsole/Console-OS_external_bluetooth_glib,ahmedammar/platform_external_gst_glib,MathieuDuponchelle/glib,zsx/glib,johne53/MB3Glib,darren-clark/android_platform_external_bluetooth_glib,lukasz-skalski/glib,lukasz-skalski/glib,johne53/MB3Glib,iConsole/Console-OS_external_bluetooth_glib,ieei/glib,MathieuDuponchelle/glib,bluez-android/glib,krichter722/glib,johne53/MB3Glib,bratsche/glib,ieei/glib-old-android,justinkb/aosp-bluez.glib,darren-clark/android_platform_external_bluetooth_glib,lukasz-skalski/glib,ieei/glib,tamaskenez/glib,tchakabam/glib,dicer/android_external_glib,Distrotech/glib,djdeath/glib,cosimoc/glib,gale320/glib,tamaskenez/glib,justinkb/aosp-bluez.glib,gale320/glib,krichter722/glib,tamaskenez/glib,johne53/MB3Glib,ieei/glib,pstglia/external-bluetooth-glib,cosimoc/glib,endlessm/glib,endlessm/glib,cention-sany/glib,johne53/MB3Glib,gale320/glib,ahmedammar/platform_external_gst_glib,endlessm/glib,antono/glib,01org/android-bluez-glib,ieei/glib,01org/android-bluez-glib,darren-clark/android_platform_external_bluetooth_glib,tamaskenez/glib,mzabaluev/glib,darren-clark/android_platform_external_bluetooth_glib,dicer/android_external_glib,tamaskenez/glib,iConsole/Console-OS_external_bluetooth_glib,pstglia/platform-external-bluetooth-glib,lukasz-skalski/glib,mzabaluev/glib,krichter722/glib,pstglia/platform-external-bluetooth-glib,cosimoc/glib,tchakabam/glib,Distrotech/glib,pstglia/external-bluetooth-glib,Distrotech/glib,iConsole/Console-OS_external_bluetooth_glib,mzabaluev/glib,pstglia/platform-external-bluetooth-glib,pstglia/external-bluetooth-glib,zsx/glib,01org/android-bluez-glib,zsx/glib,cention-sany/glib,bluez-android/glib,01org/android-bluez-glib,antono/glib,justinkb/aosp-bluez.glib,01org/android-bluez-glib,ieei/glib-old-android,cosimoc/glib,cention-sany/glib,johne53/MB3Glib,bluez-android/glib,djdeath/glib,ahmedammar/platform_external_gst_glib,mzabaluev/glib,MathieuDuponchelle/glib,cention-sany/glib,iConsole/Console-OS_external_bluetooth_glib,antono/glib,mzabaluev/glib,pstglia/platform-external-bluetooth-glib,justinkb/aosp-bluez.glib,bratsche/glib,endlessm/glib,dicer/android_external_glib,ieei/glib-old-android,dicer/android_external_glib,bratsche/glib,cention-sany/glib,endlessm/glib,pstglia/external-bluetooth-glib,bratsche/glib,darren-clark/android_platform_external_bluetooth_glib,tchakabam/glib,cosimoc/glib,krichter722/glib,MathieuDuponchelle/glib,bluez-android/glib,antono/glib,krichter722/glib,pstglia/external-bluetooth-glib,zsx/glib,tchakabam/glib,ieei/glib-old-android,MathieuDuponchelle/glib,djdeath/glib,ahmedammar/platform_external_gst_glib,tchakabam/glib,gale320/glib,gale320/glib