README: fixup typo with build instructions
Fixes up a typo here, where `make linux` builds the linux glibc-based
toolchain instead of newlib (with just `make`).
Tested, by building libtock-c apps with `make RISCV=1` - compilation OK
edit: added `make linux` with a note as some tock makefiles use
`riscv64-linux-gnu-objcopy`
@@ -135,8 +135,14 @@ Prerequisites
```
`--enable-multilib` ensures that "the multilib compiler will have the prefix riscv64-unknown-elf- or riscv64-unknown-linux-gnu- but will be able to target both 32-bit and 64-bit systems."
```
- $ sudo make linux [might need elevated privileges writing to `/opt/`]
+ $ sudo make [might need elevated privileges writing to `/opt/`]
```
+ additionally, with
+ ```
+ $ sudo make linux
+ ```
+ you can also build `riscv64-unknown-linux-gnu`, which can be useful with tock where `riscv64-unknown-linux-gnu-objcopy` is used.
+
After the the source has been compiled and copied to `/opt/riscv` and `/opt/riscv/bin`has appended to the PATH, the toolchain is ready to be used.
