Explicitly add relocation bounds to table 3 in riscv-elf.adoc

[WorldofJARcraft]

Table 3 in riscv-elf.adoc (currently section 8.4, table 9 in the latest release document) lists the target encodings and computation for all types of relocation. The table gives the type of instruction or data modified and informally states the range of the relocation (e.g., 12-bit PC-relative branch offset for BRANCH).
Based on my experience implementing RISC-V relocations for the zephyr RTOS, I think the table would be easier to read and implement if it would instead state the range of the relocation as an explicit interval, e.g., [-4096, +4094] for the BRANCH relocation.
If you agree this is useful, I will submit a PR accordingly.

[jrtc27]

That table is already pretty squished when building a PDF, so I'd worry about making it even worse by adding redundant information

[WorldofJARcraft]

The extra information might fit into the description column without increasing the size of the table too much.