Add more details when installing git repository errors

Author: 0xPoe

src/cargo/ops/common_for_install_and_uninstall.rs

@@ -612,7 +612,9 @@ where
     fn multi_err(kind: &str, mut pkgs: Vec<&Package>) -> String {
         pkgs.sort_unstable_by_key(|a| a.name());
         format!(
-            "multiple packages with {} found: {}",
+            "multiple packages with {} found: {}. When installing a git repository, \
+            cargo will always search the entire repo for any Cargo.toml. \
+            Please specify which to install.",
             kind,
             pkgs.iter()
                 .map(|p| p.name().as_str())

tests/testsuite/install.rs

@@ -414,7 +414,9 @@ fn multiple_crates_error() {
         .with_stderr(
             "\
 [UPDATING] git repository [..]
-[ERROR] multiple packages with binaries found: bar, foo
+[ERROR] multiple packages with binaries found: bar, foo. \
+When installing a git repository, cargo will always search the entire repo for any Cargo.toml. \
+Please specify which to install.
 ",
         )
         .run();