Move pages under tldr, lint run.sh, update docs

tldr/rustup-which

@@ -0,0 +1,18 @@
+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# rustup which
+
+> Display which binary will be run for a command managed by `rustup`.
+> Like `which`, but searches a Rust toolchain instead of `$PATH`.
+> More information: <https://rust-lang.github.io/rustup>.
+
+- Display the path to the binary in the default toolchain:
+
+`rustup which {{command}}`
+
+- Display the path to the binary in the specified toolchain (see `rustup help toolchain` for more information):
+
+`rustup which --toolchain {{toolchain}} {{command}}`