Minor update to `CONTRIBUTING.md` on cpplint installation. (#1023)

* Minor update to `CONTRIBUTING.md` on cpplint installation.

`cpplint` can be installed via `pip` as well as getting a local copy.
Improving documentation to include the `pip` alternative.

* Minor update to `CONTRIBUTING.md` on cpplint installation.

`cpplint` can be installed via `pip` as well as getting a local copy.
Improving documentation to include the `pip` alternative.

BUG=

* Change pip3 to pip
Co-authored-by: NTing Yan <94130036+tingyan19@users.noreply.github.com>

CONTRIBUTING.md

@@ -166,12 +166,17 @@ Below are some tips that might be useful and improve the development experience.
   is the what we do for the TFLM continuous integration Docker container.
 
 * Get a copy of [cpplint](https://github.com/google/styleguide/tree/gh-pages/cpplint)
+  or install it:
+
+  ```
+  pip install cpplint
+  ```
 
 * [yapf](https://github.com/google/yapf/) should be used for formatting Python
   code. For example:
 
   ```
-  pip3 install yapf
+  pip install yapf
   yapf log_parser.py -i --style='{based_on_style: pep8, indent_width: 2}'
   ```
 
@@ -193,7 +198,7 @@ Below are some tips that might be useful and improve the development experience.
 1.  Make sure your code is lint-free.
 
     ```
-    cpplint.py `git ls-files -m`
+    cpplint `git ls-files -m`
     ```
 
 1.  Run all the tests for x86, and any other platform that you are modifying.