Add user help on TLS 1.0/1.1 deprecation

Add context and instructions for users affected by the
TLS 1.0/1.1 deprecation.

Followup to #3411, #3293.

warehouse/templates/pages/help.html

@@ -30,12 +30,13 @@
 {% macro project_release_notifications() %}How do I get notified when a new version of a project is released?{% endmacro %}
 {% macro statistics() %}Where can I see statistics about PyPI, downloads, and project/package usage?{% endmacro %}
 {% macro login_problem() %}I forgot my PyPI password. Can you help me?{% endmacro %}
+{% macro tls_deprecation() %}Why am I getting "No matching distribution found" or "Could not fetch URL" errors during <tt>pip install</tt>?{% endmacro %}
 {% macro accessibility() %}I am having trouble using the PyPI website. Can you help me?{% endmacro %}
 {% macro uploading() %}Why can't I upload files to PyPI manually?{% endmacro %}
 {% macro private_indices() %}How can I publish my private packages to PyPI?{% endmacro %}
 {% macro admin_intervention() %}Why did my package or user registration get blocked?{% endmacro %}
 {% macro file_size_limit() %}How do I get a file size limit exemption or increase for my project?{% endmacro %}
-{% macro file_name_reuse() %}Why am I getting a "Filename or contents already exists" or "Filename has been previously used" errors?{% endmacro %}
+{% macro file_name_reuse() %}Why am I getting a "Filename or contents already exists" or "Filename has been previously used" error?{% endmacro %}
 {% macro project_name() %}Why isn't my desired project name available?{% endmacro %}
 {% macro project_name_claim() %}How do I claim an abandoned or previously registered project name?{% endmacro %}
 {% macro new_classifier() %}How do I request a new trove classifier?{% endmacro %}
@@ -77,6 +78,7 @@ <h2><a href="#integrating">Integrating</a></h2>
         <h2><a href="#problems">Problems</a></h2>
         <ul>
           <li><a href="#login-problem">{{ login_problem() }}</a></li>
+          <li><a href="#tls-deprecation">{{ tls_deprecation() }}</a></li>
           <li><a href="#accessibility">{{ accessibility() }}</a></li>
           <li><a href="#uploading">{{ uploading() }}</a></li>
           <li><a href="#private-indices">{{ private_indices() }}</a></li>
@@ -183,6 +185,14 @@ <h3 id="login-problem">{{ login_problem() }}</h3>
         </p>
         {{ code_of_conduct() }}
 
+        <h3 id="tls-deprecation">{{ tls_deprecation() }}</h3>
+        <p>
+          Transport Layer Security, or TLS, is part of how we make sure connections between your computer and PyPI are private and secure. It's a cryptographic protocol that's had several versions over time. PyPI <a href="https://mail.python.org/pipermail/python-announce-list/2018-April/011885.html">turned off support for TLS versions 1.0 and 1.1</a> in April 2018 (<a href="https://pyfound.blogspot.com/2017/01/time-to-upgrade-your-python-tls-v12.html">reason</a>). If you are having trouble with <tt> pip install</tt> and get a <tt>No matching distribution found</tt> or <tt>Could not fetch URL</tt> error, try adding <tt>-v</tt> to the command to get more information:
+        </p>
+        <p><tt>pip install --upgrade -v pip</tt>
+        </p>
+        <p>If you see an error like <tt>There was a problem confirming the ssl certificate</tt> or <tt>tlsv1 alert protocol version</tt> or <tt>TLSV1_ALERT_PROTOCOL_VERSION</tt>, you will probably need to <a href="https://pip.pypa.io/en/latest/installing/">upgrade your version of <tt>pip</tt></a> to 9.0.3 or above, which will use a more recent version of TLS. For more details, see <a href="https://mail.python.org/pipermail/python-announce-list/2018-April/011885.html">the announcement post</a> and <a href="https://github.com/pypa/warehouse/issues/3293#issuecomment-378468534">this GitHub issue</a>.</p>
+
         <h3 id="accessibility">{{ accessibility() }}</h3>
         <p>
           We take <a href="https://en.wikipedia.org/wiki/Web_accessibility" target="_blank" rel="noopener">accessibility</a> very seriously and want to make the website easy to use for everyone.