add example for a persistent session and logging into a webform (#686)

docs/examples/session.jl

@@ -0,0 +1,14 @@
+"""
+A simple example of creating a persistent session and logging into a web form. HTTP.jl does not have a distinct session object like requests.session() or rvest::html_session() but rather uses the `cookies` flag along with standard functions
+"""
+using HTTP
+
+#dummy site, any credentials work
+url = "http://quotes.toscrape.com/login"
+session = HTTP.get(url; cookies = true)
+
+credentials = Dict(
+    "Username" => "username",
+    "Password" => "password")
+
+response = HTTP.post(url, credentials)