Fix the literal blocks

pep-0470.txt

@@ -84,31 +84,36 @@ Examples of Additional indexes with pip
 
 **Invocation:**
 
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+::
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     $ pip install --extra-index-url https://pypi.example.com/ foobar
 
 **Shell Environment:**
 
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     $ export PIP_EXTRA_INDEX_URL=https://pypi.example.com/
     $ pip install foobar
 
 **Requirements File:**
 
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     $ echo "--extra-index-url https://pypi.example.com/\nfoobar" > requirements.txt
     $ pip install -r requirements.txt
 
 **Virtual Environment:**
 
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+::
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     $ python -m venv myvenv
     $ echo "[global]\nextra-index-url = https://pypi.exmaple.com/" > myvenv/pip.conf
     $ myvenv/bin/pip install foobar
 
 **User:**
 
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+::
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     $ echo "[global]\nextra-index-url = https://pypi.exmaple.com/" >~/.pip/pip.conf
     $ pip install foobar