[Infra] Fix hardfloat module path.

.gitmodules

@@ -1,6 +1,6 @@
 [submodule "fu/pymtl3_hardfloat"]
 	path = fu/pymtl3_hardfloat
-	url = git@github.com:pymtl/pymtl3-hardfloat.git
+	url = https://github.com/pymtl/pymtl3-hardfloat.git
 [submodule "fu/dp_fpfma"]
 	path = fu/dp_fpfma
 	url = https://github.com/tancheng/dp_fpfma

README.md

@@ -105,7 +105,6 @@ We can now use git to clone the VectorCGRA repo.
  % git clone https://github.com/tancheng/VectorCGRA.git
  % git submodule update --init
 ```
-Note that if the submodule update fails, try change the `url` of `[submodule "fu/pymtl3_hardfloat"]` in the `.git/config` from `[email protected]:pymtl/pymtl3-hardfloat.git` to `https://github.com/pymtl/pymtl3-hardfloat.git`.
 
 ### Run an example to generate Verilog