added template for author update view

bookshelf/templates/bookshelf/edit-author.html

+{% extends 'base.html' %}
+
+{% block title %}Edit Author{% endblock %}
+{% block header %}Edit Author{%  endblock %}
+{% block content %}
+    <form method="post">
+    {% csrf_token %}
+    {{ form.as_p }}
+        <input type="submit" value="Save Changes">
+    </form>
+{% endblock %}
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