Add an MSRV

This just copies TaskChampion's MSRV for the moment.

.github/workflows/rust-tests.yml

@@ -13,6 +13,8 @@ jobs:
       # A simple matrix for now, but if we introduce an MSRV it can be added here.
       matrix:
         rust:
+          # MSRV
+          - "1.81.0"
           - "stable"
 
     runs-on: ubuntu-latest

Cargo.toml

@@ -5,6 +5,7 @@ members = [
   "server",
   "sqlite",
 ]
+rust-version = "1.81.0" # MSRV
 
 [workspace.dependencies]
 uuid = { version = "^1.13.1", features = ["serde", "v4"] }

README.md

@@ -103,7 +103,11 @@ release version. You can install Rust from your distribution package or use
 rustup default stable
 ```
 
-If you prefer, you can use the stable version only for install TaskChampion
+The minimum supported Rust version (MSRV) is given in
+[`Cargo.toml`](./Cargo.toml). Note that package repositories typically do not
+have sufficiently new versions of Rust.
+
+If you prefer, you can use the stable version only for installing TaskChampion
 Sync-Server (you must clone the repository first).
 ```sh
 rustup override set stable