doc: Make File store/get integer methods clearer
doc: Make File store/get integer methods clearer

Add an example on how to store signed integers on less than 64 bits,
using one bit for the signedness.

honix/godot,guilhermefelipecgs/godot,Zylann/godot,honix/godot,Zylann/godot,Shockblast/godot,firefly2442/godot,ZuBsPaCe/godot,pkowal1982/godot,honix/godot,MarianoGnu/godot,BastiaanOlij/godot,vkbsb/godot,godotengine/godot,sanikoyes/godot,BastiaanOlij/godot,ZuBsPaCe/godot,sanikoyes/godot,Faless/godot,akien-mga/godot,DmitriySalnikov/godot,Shockblast/godot,sanikoyes/godot,MarianoGnu/godot,josempans/godot,BastiaanOlij/godot,firefly2442/godot,Zylann/godot,MarianoGnu/godot,ZuBsPaCe/godot,Shockblast/godot,Paulloz/godot,sanikoyes/godot,pkowal1982/godot,vkbsb/godot,vnen/godot,godotengine/godot,Valentactive/godot,Paulloz/godot,akien-mga/godot,Shockblast/godot,pkowal1982/godot,akien-mga/godot,MarianoGnu/godot,ZuBsPaCe/godot,DmitriySalnikov/godot,guilhermefelipecgs/godot,Valentactive/godot,josempans/godot,Paulloz/godot,Paulloz/godot,Valentactive/godot,akien-mga/godot,vkbsb/godot,firefly2442/godot,MarianoGnu/godot,josempans/godot,vkbsb/godot,akien-mga/godot,MarianoGnu/godot,DmitriySalnikov/godot,Faless/godot,josempans/godot,ZuBsPaCe/godot,firefly2442/godot,Paulloz/godot,josempans/godot,ZuBsPaCe/godot,pkowal1982/godot,vnen/godot,vnen/godot,Zylann/godot,DmitriySalnikov/godot,DmitriySalnikov/godot,firefly2442/godot,guilhermefelipecgs/godot,vkbsb/godot,guilhermefelipecgs/godot,Zylann/godot,vnen/godot,Faless/godot,Faless/godot,sanikoyes/godot,firefly2442/godot,Valentactive/godot,sanikoyes/godot,josempans/godot,Faless/godot,vkbsb/godot,Shockblast/godot,MarianoGnu/godot,guilhermefelipecgs/godot,ZuBsPaCe/godot,Faless/godot,Paulloz/godot,BastiaanOlij/godot,godotengine/godot,godotengine/godot,BastiaanOlij/godot,akien-mga/godot,Zylann/godot,sanikoyes/godot,pkowal1982/godot,guilhermefelipecgs/godot,Shockblast/godot,MarianoGnu/godot,honix/godot,BastiaanOlij/godot,vkbsb/godot,Zylann/godot,firefly2442/godot,Shockblast/godot,godotengine/godot,vkbsb/godot,Zylann/godot,BastiaanOlij/godot,DmitriySalnikov/godot,godotengine/godot,pkowal1982/godot,Valentactive/godot,godotengine/godot,Valentactive/godot,pkowal1982/godot,akien-mga/godot,Shockblast/godot,godotengine/godot,josempans/godot,Valentactive/godot,BastiaanOlij/godot,vnen/godot,vnen/godot,Valentactive/godot,honix/godot,Faless/godot,akien-mga/godot,guilhermefelipecgs/godot,vnen/godot,guilhermefelipecgs/godot,vnen/godot,pkowal1982/godot,Faless/godot,ZuBsPaCe/godot,Paulloz/godot,sanikoyes/godot,firefly2442/godot,honix/godot,DmitriySalnikov/godot,josempans/godot