Some final edits to the documentation

The first pass, where I just ran Vale on things to see where it got me,
still had room for improvement.

I even "fixed" an instance of passive voice by introducing an obvious
(in retrospect) grammatical error. Neat.

Author: ahamlinman

README.md

@@ -24,7 +24,7 @@ You'll need the [Go][go] toolchain installed to try the demo program.
 1. See what to do next: `./randomizer-demo help`
 
 The demo saves groups in a [bbolt][bbolt] database in the current directory,
-and outputs responses using [Slack's message formatting][format]. This gives a
+and outputs responses using [Slack's "mrkdwn" format][format]. This gives a
 taste of how the command works, and helps with testing.
 
 [go]: https://golang.org/
@@ -38,9 +38,8 @@ Slack:
 
 - `SERVERLESS.md` is a detailed walkthrough for deployment on [AWS
   Lambda][lambda], Amazon's managed function as a service platform.
-- `SERVERMORE.md` is a high-level guide for setting up the `randomizer-server`
-  HTTP server, that assumes more background knowledge and/or willingness to
-  dive into details of both standard server management and the randomizer
-  implementation.
+- `SERVERMORE.md` is a high-level guide for configuring the `randomizer-server`
+  HTTP server. It assumes more background knowledge and/or willingness to dive
+  into the details of server management and the randomizer implementation.
 
 [lambda]: https://aws.amazon.com/lambda/

SERVERLESS.md

@@ -130,7 +130,7 @@ Run `./hfc help` to learn more about additional commands that might be useful.
   transformation to simplify the setup of the Lambda function.
 - The template provisions the DynamoDB table in On-Demand capacity mode, which
   isn't eligible for the AWS Free Tier. See the [Read/Write Capacity
-  Mode][capacity mode] documentation for more details.
+  Mode][capacity mode] documentation for details.
 - The default configuration enables [AWS X-Ray][x-ray] tracing for the function
   and its requests to DynamoDB. X-Ray is free for up to 100,000 traces per month
   for every AWS account, and it's useful to see where each request is spending

SERVERMORE.md

@@ -14,8 +14,8 @@ This guide **doesn't** cover:
   you wish to use a cloud provider for group storage or secrets.
 
 If you're uncomfortable with these topics or the rest of this guide, and you
-aren't interested in learning them, the AWS Lambda setup might be preferable
-(see `SERVERLESS.md`).
+aren't interested in learning them, you might prefer the AWS Lambda setup in
+`SERVERLESS.md`.
 
 In addition to the environment variables below, see `randomizer-server -help`
 for CLI flags that you may wish to set, like the bind address for the server
@@ -73,7 +73,7 @@ operational ease comparable to the AWS Lambda solution (though the randomizer
 doesn't include infrastructure-as-code for it out of the box).
 
 The Firestore backend requires a pre-existing database in a Google Cloud
-project (only Native mode been tested, but Datastore mode may work too).
+project (only Native mode has been tested, but Datastore mode may work too).
 Note that the randomizer expects to use the full database, and that only the
 "(default)" database in each Google Cloud project is eligible for the Firestore
 free tier.