[DOCS] update installation doc and add gitignore (#279)

Co-authored-by: Min Xu <min.xu.public@gmail.com>

docs/getting-started/installation.rst

@@ -44,6 +44,7 @@ You can then test your installation by running the unit tests:
 
 .. code-block:: bash
 
+      pip install -r requirements-test.txt
       pytest -vs .
 
 and the benchmarks
@@ -51,4 +52,4 @@ and the benchmarks
 .. code-block:: bash
       
       cd bench/
-      python -m run --with-plots --result-dir /tmp/triton-bench
+      python -m run --with-plots --result-dir /tmp/triton-bench