.github: add default PR template

Based on the .github/PULL_REQUEST_TEMPLATE file in the main Go repo
at commit e4283592e5cb00d84544df2442b0d3f4eccf8c72 (go.dev/cl/777780),
with modifications to make it a better fit for most golang.org/x repos.

- changed the wiki page link

Fixes golang/go#79215

Change-Id: I68dbaa75f384fce54a8ab502b82cdfb341b53766
Reviewed-on: https://go-review.googlesource.com/c/dot-github/+/781541
TryBot-Bypass: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Bypass: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
new file mode 100644
index 0000000..7df6858
--- /dev/null
+++ b/.github/pull_request_template.md
@@ -0,0 +1,27 @@
+This PR will be imported into Gerrit with the title and first
+comment (this text) used to generate the subject and body of
+the Gerrit change.
+
+**Please ensure you adhere to every item in this list.**
+
+More info can be found at https://go.dev/wiki/CommitMessage
+
++ The PR title is formatted as follows: `net/http: frob the quux before blarfing`
+  + The package name goes before the colon
+  + The part after the colon uses the verb tense + phrase that completes the blank in,
+    "This change modifies Go to ___________"
+  + Lowercase verb after the colon
+  + No trailing period
+  + Keep the title as short as possible, ideally 72 characters or shorter
++ No Markdown
++ The first PR comment (this one) is wrapped at around 72 characters, unless it's
+  really needed (ASCII art, table, or long link)
++ If there is a corresponding issue,
+  add either `Fixes golang/go#1234` or `Updates golang/go#1234`
+  (the latter if this is not a complete fix) to this comment
++ Most Go repositories use the main issue tracker in the `golang/go` repo.
+  If this PR is for a repository with a dedicated issue tracker,
+  use the `owner/repo#issue_number` syntax: `Fixes golang/vscode-go#1234`
++ We do not use Signed-off-by lines in Go. Please don't add them.
+  Our Gerrit server & GitHub bots enforce CLA compliance instead.
++ Delete these instructions once you have read and applied them
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..746504c
--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+## .github
+
+Default community health files for the Go repositories in GitHub.