feat(forge/install): take root flag (gakonst#580)

cli/src/cmd/install.rs

@@ -1,8 +1,9 @@
 //! Create command
+use std::path::PathBuf;
 
 use crate::{cmd::Cmd, opts::forge::Dependency, utils::p_println};
 use ansi_term::Colour;
-use clap::Parser;
+use clap::{Parser, ValueHint};
 use foundry_config::find_project_root_path;
 use std::{
     path::Path,
@@ -16,13 +17,21 @@ pub struct InstallArgs {
     dependencies: Vec<Dependency>,
     #[clap(flatten)]
     opts: DependencyInstallOpts,
+    #[clap(
+        help = "the project's root path. By default, this is the root directory of the current Git repository or the current working directory if it is not part of a Git repository",
+        long,
+        value_hint = ValueHint::DirPath
+    )]
+    pub root: Option<PathBuf>,
 }
 
 impl Cmd for InstallArgs {
     type Output = ();
 
     fn run(self) -> eyre::Result<Self::Output> {
-        install(find_project_root_path()?, self.dependencies, self.opts)
+        let InstallArgs { root, .. } = self;
+        let root = root.unwrap_or_else(|| find_project_root_path().unwrap());
+        install(root, self.dependencies, self.opts)
     }
 }