feat(runtime): add missing doc comments on Shell

Signed-off-by: Charlotte Meyer <dev@buffet.sh>

crates/oyster_runtime/src/lib.rs

@@ -71,6 +71,8 @@ pub struct Shell {
 }
 
 impl Shell {
+    /// Create a new shell.
+    /// This also sets up the *global* signal handlers.
     pub fn new() -> Result<Shell, nix::Error> {
         let ignore = SigAction::new(SigHandler::SigIgn, SaFlags::empty(), SigSet::empty());
 
@@ -85,10 +87,12 @@ impl Shell {
         })
     }
 
+    /// Returns true if the shell is supposed to still be running.
     pub fn is_running(&self) -> bool {
         self.is_running
     }
 
+    /// Runs a given program.
     pub fn run<'a>(&mut self, code: &'a ast::Code) -> Result<Status, RuntimeError> {
         let mut last_status = Status::SUCCESS;
 
@@ -101,6 +105,7 @@ impl Shell {
         Ok(last_status)
     }
 
+    /// Runs a given program in a seperate process, and returns its output.
     pub fn run_subshell<'a>(&mut self, code: &'a ast::Code) -> Result<OsString, RuntimeError> {
         let (output, input) =
             unistd::pipe2(OFlag::empty()).map_err(RuntimeError::PipeCreationFailed)?;