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>

docs/Chipyard-Basics/Initial-Repo-Setup.rst

@@ -34,6 +34,9 @@ After cloning this repo, you will need to initialize all of the submodules.
     cd chipyard
     ./scripts/init-submodules-no-riscv-tools.sh
 
+When updating Chipyard to a new version, you will also want to rerun this script to update the submodules.
+Using git directly will try to initialize all submodules; this is not recommended unless you expressly desire this behavior.
+
 .. _build-toolchains:
 
 Building a Toolchain