add in aws sdk and docs for aws policy

Dockerfile

@@ -1,10 +1,11 @@
 FROM library/alpine:3.5
 
 # deps - python openssl curl sed grep mktemp
+# boto 3 - AWS SDK for python
 RUN apk add --no-cache --virtual .build-deps git \
     && apk add --no-cache --virtual .dehydrated-rundeps python py2-pip bash openssl curl \
     && pip install --upgrade pip \
-    && pip install dns-lexicon dns-lexicon[route53] dns-lexicon[transip] \
+    && pip install dns-lexicon boto3 dns-lexicon[route53] dns-lexicon[transip] \
     && cd /tmp \
     && git clone https://github.com/lukas2511/dehydrated.git --depth 1 \
     && chmod a+x dehydrated/dehydrated \

README.md

@@ -24,9 +24,15 @@ COPY config /etc/dehydrated/config
 # defaults to `staging`, use `production` when ready.
 LE_ENV=staging
 # Only required if you plan to use dns-01 challenges (use for private services)
+# CloudFlare example
 PROVIDER=cloudflare
 LEXICON_CLOUDFLARE_USERNAME=
 LEXICON_CLOUDFLARE_TOKEN=
+
+# Route 53 example
+PROVIDER=route53
+LEXICON_ROUTE53_ACCESS_KEY=
+LEXICON_ROUTE53_ACCESS_SECRET=
 ```
 
 ## Testing
@@ -81,5 +87,23 @@ docker run -d \
         --challenge http-01
 ```
 
+## Route53 Access Policy
+```json
+{
+    "Version": "2012-10-17",
+    "Statement": [
+        {
+            "Effect": "Allow",
+            "Action": [
+                "route53:ListHostedZonesByName",
+                "route53:ChangeResourceRecordSets"
+            ],
+            "Resource": [
+                "*"
+            ]
+        }
+    ]
+}
+```
 
 Note: `certbot/make_letsencrypt_cert` is an alternate method that one could use with the certbot docker image. However dns-01 is not supported.