Document linkerscript format in manpage

Signed-off-by: AntonioND <antonio_nd@outlook.com>

src/link/rgblink.5

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+.Dd March 27, 2017
+.Dt RGBLINK 5
+.Os RGBDS Manual
+.Sh NAME
+.Nm rgblink
+.Nd linkerscript file format
+.Sh DESCRIPTION
+The linkerscript is an external file that allows the user to specify the
+order of sections without the need for doing so before assembling each object
+file.
+.Pp
+The placement of sections specified in the linkerscript is done before the
+sections whose placement is defined in the source code.
+.Pp
+A linkerscript consists on a series of banks followed by a list of sections
+and, optionally, commands.
+They can be lowercase or uppercase, it is ignored.
+Any line can contain a comment starting with
+.Ql \&;
+that ends at the end of the line:
+.Pp
+  ROMX $F ; This is a comment
+   "Functions to read array"
+   ALIGN 8
+   "Array aligned to 256 bytes"
+
+  WRAMX 2
+    "Some variables"
+.Pp
+Numbers can be in decimal or hexadecimal format (the prefix is
+.Ql $ ) .
+It is an error if any bank or command is found before setting a bank.
+.Pp
+The possible bank types are: ROM0, ROMX, VRAM, WRAM0, WRAMX, OAM and HRAM.
+Types ROMX, VRAM, WRAMX and SRAM are banked, which means that it is needed to
+specify a bank after the type.
+.Pp
+When a new bank statement is found, sections found after it will be placed
+right from the beginning of that bank.
+If the linkerscript switches to a different bank and then it comes back to the
+previous one it will continue from the last address that was used.
+.Pp
+The only two commands are ORG and ALIGN:
+.Bl -bullet
+.It
+ORG sets the address in which new sections will be placed.
+It can not be lower than the current address.
+.It
+ALIGN will increase the address until it is aligned to the specified boundary
+(it tries to set to 0 the number of bits specified after the command: ALIGN 8
+will align to $100).
+.El
+.Pp
+Note: The bank, alignment, address and type of sections can be specified both
+in the source code and in the linkerscript.
+For a section to be able to be placed with the linkerscript the bank must be
+left unassigned in the source code or be the same as the one specified in the
+linkerscript. The address and alignment musn't be set.
+.Sh SEE ALSO
+.Xr rgbasm 1 ,
+.Xr rgblink 1 ,
+.Xr rgbfix 1 ,
+.Xr rgbds 7
+.Sh HISTORY
+.Nm
+was originally written by Carsten S\(/orensen as part of the ASMotor package,
+and was later packaged in RGBDS by Justin Lloyd. It is now maintained by a
+number of contributors at https://github.com/rednex/rgbds.