chore(devops): Ignore node_modules and temp files (#19)

# Motivation
`git status` shows uninteresting results: `node_modules` and temp files
show up. Also, a placeholder `assets.tar.gz` is created but is not
needed; that is inherited from the nns-dapp.

# Changes
- Ignore the node_modules directory and temp files with names starting
with , (comma).
- Don't create the `assets.tar.gz`

# Tests
Running git-status locally now shows cleaner output.

.gitignore

@@ -1,5 +1,7 @@
 # Rust build artefacts
 /target
+# npm dependencies
+node_modules
 # Testing tool
 pocket-ic
 pocket-ic.gz
@@ -11,3 +13,5 @@ pocket-ic.gz
 branches
 # Build artefacts
 out
+# Temp files
+,*

scripts/lint-rs

@@ -1,6 +1,4 @@
 #!/usr/bin/env bash
 set -euo pipefail
-# Craete an empty assets file, if there is none.
-test -e assets.tar.xz || touch assets.tar.xz
 # Lint the rust code
 cargo clippy --locked --target wasm32-unknown-unknown --all-features -- -D warnings -W clippy::pedantic -A clippy::module-name-repetitions -A clippy::struct-field-names -A clippy::missing_errors_doc