_content/doc: fix module and tutorial bugs and clean up flow

For golang/go#44241

- Fix issues 2, 3, 8, 16, 17, 18 from golang/go#44241

Other changes in multiple topics:

- In markdown, replace HTML anchor tags with {#anchor} tags.
- In a few places, add content to clarify that module path must
  be a location from which the module can be downloaded.
- Where it was missing, add example.com domain to example module
  paths. Hopefully, this will reinforce the idea that the module
  path should typically include a domain. Docs will use
  something that looks like a domain name for module path.
- Add more cross-references from tutorial to references for
  packages and commands.
- Rewrite a few links so that they include the topic title,
  rather than simply inline text. Left those links whose
  destinations are references -- the item's name seems to
  suggest that a reference is at the destination.
- Remove domain name from golang.org doc links, leaving root
  directory. Such as /cmd/go/* or /doc/modules/*
- Add path up to root for all links in the same domain.
  Some were linking by file name only.
- Change standard library links from golang.org to pkg.go.dev.

Changes in the module tutorial:

- Add text to help clarify that there should be a hello and
  greetings directory as siblings in their directory hierarchy.
  Some users thought one should be subordinate to the other.
- Where needed, reorder steps so that `go mod init` is run before
  code is added. This is intended to reinforce the importance of
  the module's presence.
- In require/replace steps, have the user use `go mod edit`
  rather than editing the go.mod file in an editor. The tools
  are more likely to yield a functioning result.
- Where possible/appropriate, change module directive link
  destinations from "Modules reference" to go.mod reference.
- Change "run the code" steps so that they all use `go run .`
  rather than `go build` or `go run <filename>`. This removes
  the impedance of explanation and more commands, while
  moving the explanation of `go build` and `go install` to
  a separate topic where they share a clearer context.
- Add a "Conclusion" topic with a few links. The tutorial ended
  rather abruptly before.
- Minor edits to remove some redundant language.

Change-Id: I93055035d73c362ba73edea458fc53bc45e66512
Reviewed-on: https://go-review.googlesource.com/c/website/+/297531
Trust: Steve Traut <straut@google.com>
Run-TryBot: Steve Traut <straut@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 10 insertions, 9 deletions

diff --git a/_content/doc/code.html b/_content/doc/code.html
index a1b9bd20..99a1729a 100644
--- a/_content/doc/code.html
+++ b/_content/doc/code.html
@@ -78,7 +78,7 @@ go: creating new go.mod: module example.com/user/hello
 $ cat go.mod
 module example.com/user/hello
 
-go 1.14
+go 1.16
 $
 </pre>
 
@@ -323,16 +323,17 @@ func main() {
 </pre>
 
 <p>
-When you run commands like <code>go install</code>, <code>go build</code>, or
-<code>go run</code>, the <code>go</code> command will automatically download the
-remote module and record its version in your <code>go.mod</code> file:
+Now that you have a dependency on an external module, you need to download that
+module and record its version in your <code>go.mod</code> file. The <code>go
+mod tidy</code> command adds missing module requirements for imported packages
+and removes requirements on modules that aren't used anymore.
 </p>
 
 <pre>
-$ go install example.com/user/hello
+$ go mod tidy
 go: finding module for package github.com/google/go-cmp/cmp
-go: downloading github.com/google/go-cmp v0.4.0
-go: found github.com/google/go-cmp/cmp in github.com/google/go-cmp v0.4.0
+go: found github.com/google/go-cmp/cmp in github.com/google/go-cmp v0.5.4
+$ go install example.com/user/hello
 $ hello
 Hello, Go!
   string(
@@ -342,9 +343,9 @@ Hello, Go!
 $ cat go.mod
 module example.com/user/hello
 
-go 1.14
+go 1.16
 
-<b>require github.com/google/go-cmp v0.4.0</b>
+<b>require github.com/google/go-cmp v0.5.4</b>
 $
 </pre>