examples: separate code files in code.dvc.org/tutorial-nlp, and

1. for tutorial preparation
2. for get-started example-pipeline
(soon both will be merged, see #564

AND standardize venv+pip install instructions throughout docs

static/docs/commands-reference/import-url.md

@@ -261,8 +261,8 @@ $ rm -f code.zip
 
 ### Click and expand to setup the environment
 
-For this step we'll need to install the project requirements. For that we
-**strongly** recommend creating a virtual environment with a tool such as
+Let's install the requirements. But before we do that, we **strongly** recommend
+creating a virtual environment with a tool such as
 [virtualenv](https://virtualenv.pypa.io/en/stable/):
 
 ```dvc

static/docs/get-started/connect-code-and-data.md

@@ -40,20 +40,20 @@ $ tree
     └── train.py
 ```
 
-We **strongly** recommend using
-[virtualenv](https://virtualenv.pypa.io/en/stable/) or a similar tool to isolate
-your environment:
+Now let's install the requirements. But before we do that, we **strongly**
+recommend creating a virtual environment with a tool such as
+[virtualenv](https://virtualenv.pypa.io/en/stable/):
 
 ```dvc
-$ virtualenv .env
-$ echo ".env/" >> .gitignore
+$ virtualenv -p python3 .env
 $ source .env/bin/activate
+$ echo ".env/" >> .gitignore
+$ pip install -r requirements.txt
 ```
 
-Now, we are ready to install dependencies to run the code:
+Save the progress to Git:
 
 ```dvc
-$ pip install -U -r requirements.txt
 $ git add .
 $ git commit -m "add code"
 ```

static/docs/get-started/example-pipeline.md

@@ -38,27 +38,22 @@ your browser to download `code.zip`.
 ```dvc
 $ mkdir example && cd example
 $ git init
-$ wget https://code.dvc.org/tutorial-nlp/code.zip
+$ wget https://code.dvc.org/tutorial-nlp/pipeline.zip
 $ unzip code.zip
 $ rm -f code.zip
 $ git add code/
 $ git commit -m "download and initialize code"
 ```
 
-(Optional) It's highly recommended to initialize a virtual environment with
-[virtualenv](https://virtualenv.pypa.io/en/stable/) or a similar tool to keep
-your global packages clean and untouched:
+Now let's install the requirements. But before we do that, we **strongly**
+recommend creating a virtual environment with a tool such as
+[virtualenv](https://virtualenv.pypa.io/en/stable/):
 
 ```dvc
-$ virtualenv .env
+$ virtualenv -p python3 .env
 $ source .env/bin/activate
 $ echo ".env/" >> .gitignore
-```
-
-Install the required dependencies:
-
-```dvc
-$ pip install -r code/requirements.txt
+$ pip install -r requirements.txt
 ```
 
 Next, we will create a pipeline step-by-step, utilizing the same set of commands

static/docs/get-started/example-versioning.md

@@ -46,19 +46,14 @@ $ cd example-versioning
 This command pulls a repository with a single script `train.py` that runs the
 training.
 
-(Optional) It's highly recommended to initialize a virtual environment with
-[virtualenv](https://virtualenv.pypa.io/en/stable/) or a similar tool to keep
-your global packages clean and untouched:
+Now let's install the requirements. But before we do that, we **strongly**
+recommend creating a virtual environment with a tool such as
+[virtualenv](https://virtualenv.pypa.io/en/stable/):
 
 ```dvc
-$ virtualenv .env
+$ virtualenv -p python3 .env
 $ source .env/bin/activate
 $ echo ".env/" >> .gitignore
-```
-
-Install required dependencies:
-
-```dvc
 $ pip install -r requirements.txt
 ```
 

static/docs/tutorial/preparation.md

@@ -26,26 +26,21 @@ download `code.zip`.
 $ mkdir classify
 $ cd classify
 $ git init
-$ wget https://dvc.org/s3/so/code.zip
+$ wget https://code.dvc.org/tutorial-nlp/code.zip
 $ unzip code.zip -d code && rm -f code.zip
 $ git add code/
 $ git commit -m "download code"
 ```
 
-(Optional) It's highly recommended to initialize a virtual environment with
-[virtualenv](https://virtualenv.pypa.io/en/stable/) or a similar tool to keep
-your global packages clean and untouched:
+Now let's install the requirements. But before we do that, we **strongly**
+recommend creating a virtual environment with a tool such as
+[virtualenv](https://virtualenv.pypa.io/en/stable/):
 
 ```dvc
-$ virtualenv .env
+$ virtualenv -p python3 .env
 $ source .env/bin/activate
-$ echo ".env/" >> .git/info/exclude
-```
-
-Install the code requirements:
-
-```dvc
-$ pip install -r code/requirements.txt
+$ echo ".env/" >> .gitignore
+$ pip install -r requirements.txt
 ```
 
 ## Install DVC

static/docs/user-guide/contributing.md

@@ -47,7 +47,7 @@ install Python.
 Install DVC in editable mode with `pip install -e ".[all,tests]"`. We
 **strongly** recommend initializing a
 [virtual environment](https://virtualenv.pypa.io/en/latest/userguide/) before
-installing the required libraries. For example:
+doing so:
 
 ```dvc
 $ cd dvc