[Fixes #12] Mark outdated nature of Hardware Revision A (#13)

* [Fixes #12] Use different `README.md` template for revision A
* [Fixes #12] Amend the `README.md.revA.template` file
    The modification explains the **Hardware Revision A** refers to potentially outdated chip variant no longer manufactured.
* [Fixes #12] Address review suggestions

pac/README.md.revA.template

@@ -0,0 +1,9 @@
+# Peripheral Access Crate ${crate} for ${mcu} 32-bit MCU from Atmel/Microchip
+
+This PAC crate relates to **Hardware Revision A** that has been superseded by **Hardware Revision B** (refer to the [`${crate}b`](https://https://crates.io/crates/${crate}b) crate). The former is no longer in production.
+
+This crate contains autogenerated code to access peripherals of ${mcu} generated from official SVD files from Microchip mirrored at [posborne/cmsis-svd](https://github.com/posborne/cmsis-svd) using [svd2rust](https://github.com/rust-embedded/svd2rust/) tool.
+
+## License
+
+[BSD Zero Clause License](https://choosealicense.com/licenses/0bsd/)

update.py

@@ -3,15 +3,16 @@
 
 def generate_cargo(crate: str, location: pathlib.Path):
     template = ""
-    with open("Cargo.toml.template") as templatefile:
+    with open("pac/Cargo.toml.template") as templatefile:
         template = templatefile.read()
     with open(location.joinpath("Cargo.toml"), "w") as cargotomlfile:
         cargotomlcontent = string.Template(template).substitute(crate=crate, mcu=crate.upper())
         cargotomlfile.write(cargotomlcontent)
 
 def generate_readme(crate: str, location: pathlib.Path):
     template = ""
-    with open("README.md.template") as templatefile:
+    template_filename = "pac/README.md.template" if crate[-1:] == 'b' else "pac/README.md.revA.template" 
+    with open(template_filename) as templatefile:
         template = templatefile.read()
     with open(location.joinpath("README.md"), "w") as cargotomlfile:
         cargotomlcontent = string.Template(template).substitute(crate=crate, mcu=crate.upper())