Merge #88: Pin proc-macro2 and quote in CI for MSRV purposes

3c0718c Explain how to build with the MSRV in the README (Daniela Brozzoni)
9793017 Pin proc-macro2 and quote in CI for MSRV purposes (Daniela Brozzoni)

Pull request description:

ACKs for top commit:
  afilini:
    ACK 3c0718c

Tree-SHA512: 7220c4cd9b3078effbcad1371b2f4fd3fe810b1f6a2f73b7bd14c0ee93d704b8e8193eeca889c5bcd4200cdcdcadd6d1ee6ae704cf2a43b17e88cf424ed30bc2

Author: danielabrozzoni

.github/workflows/main.yml

@@ -89,7 +89,8 @@ jobs:
         # serde 1.0.157 uses syn 2.0 which requires edition 2021.
         # serde_json depends on 1.0.66
         # once_cell v0.15.0 uses edition 2021.
-        run: cargo update -p serde_json --precise 1.0.99 && cargo update -p serde --precise 1.0.156  && cargo update -p once_cell --precise 1.14.0
+        # quote 1.0.31 uses proc-macro2 1.0.66, which requires edition 2021
+        run: cargo update -p serde_json --precise 1.0.99 && cargo update -p serde --precise 1.0.156  && cargo update -p once_cell --precise 1.14.0 && cargo update -p quote --precise 1.0.30 && cargo update -p proc-macro2 --precise 1.0.65
 
       - name: Test
         run: cargo test --features ${{ matrix.rust.features }}

README.md

@@ -10,7 +10,14 @@ This library internally uses PyO3 to call HWI's functions. It is not a re-implem
 
 ## MSRV
 
-The MSRV for this project is `1.48.0`.
+The MSRV for this project is `1.48.0`. To build with the MSRV you will need to pin some dependencies:
+```bash
+cargo update -p serde_json --precise 1.0.99
+cargo update -p serde --precise 1.0.156
+cargo update -p once_cell --precise 1.14.0
+cargo update -p quote --precise 1.0.30
+cargo update -p proc-macro2 --precise 1.0.65
+```
 
 ## Prerequisites