Add a git version check to the init scripts and make them work outside of the repo root. (#459)

* Fixes #453

- Update scripts/init-submodules-no-riscv-tools.sh to also work if you're in scripts/

- Provide a git version check to ensure the init scripts will work (>= 1.7.8)

- Update the documentation to be more explicit that the init script is also for updating.

* Update scripts/init-submodules-no-riscv-tools-nolog.sh

Co-Authored-By: Albert Ou <aou@eecs.berkeley.edu>

scripts/init-submodules-no-riscv-tools.sh

@@ -5,4 +5,7 @@
 set -e
 set -o pipefail
 
+RDIR=$(git rev-parse --show-toplevel)
+cd "$RDIR"
+
 ./scripts/init-submodules-no-riscv-tools-nolog.sh "$@" 2>&1 | tee init-submodules-no-riscv-tools.log