chore: update PR template (#221)

This PR was generated using Autosynth. 🌈


<details><summary>Log from Synthtool</summary>

```
2020-03-13 14:40:51,913 synthtool > Executing /tmpfs/src/git/autosynth/working_repo/synth.py.
2020-03-13 14:40:51,973 synthtool > Ensuring dependencies.
2020-03-13 14:40:51,980 synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:f54b7644a1d2e7a37b23f5c0dfe9bba473e41c675002a507a244389e27487ca9
Status: Image is up to date for googleapis/artman:latest
.github/ISSUE_TEMPLATE/bug_report.md
.github/ISSUE_TEMPLATE/feature_request.md
.github/ISSUE_TEMPLATE/support_request.md
.github/PULL_REQUEST_TEMPLATE.md
.github/release-please.yml
.github/trusted-contribution.yml
.kokoro/build.bat
.kokoro/build.sh
.kokoro/coerce_logs.sh
.kokoro/common.cfg
.kokoro/continuous/common.cfg
.kokoro/continuous/dependencies.cfg
.kokoro/continuous/integration.cfg
.kokoro/continuous/java11.cfg
.kokoro/continuous/java7.cfg
.kokoro/continuous/java8-osx.cfg
.kokoro/continuous/java8-win.cfg
.kokoro/continuous/java8.cfg
.kokoro/continuous/lint.cfg
.kokoro/continuous/propose_release.cfg
.kokoro/continuous/samples.cfg
.kokoro/dependencies.sh
.kokoro/linkage-monitor.sh
.kokoro/nightly/common.cfg
.kokoro/nightly/dependencies.cfg
.kokoro/nightly/integration.cfg
.kokoro/nightly/java11.cfg
.kokoro/nightly/java7.cfg
.kokoro/nightly/java8-osx.cfg
.kokoro/nightly/java8-win.cfg
.kokoro/nightly/java8.cfg
.kokoro/nightly/lint.cfg
.kokoro/nightly/samples.cfg
.kokoro/presubmit/clirr.cfg
.kokoro/presubmit/common.cfg
.kokoro/presubmit/dependencies.cfg
.kokoro/presubmit/integration.cfg
.kokoro/presubmit/java11.cfg
.kokoro/presubmit/java7.cfg
.kokoro/presubmit/java8-osx.cfg
.kokoro/presubmit/java8-win.cfg
.kokoro/presubmit/java8.cfg
.kokoro/presubmit/linkage-monitor.cfg
.kokoro/presubmit/lint.cfg
.kokoro/presubmit/samples.cfg
.kokoro/release/bump_snapshot.cfg
.kokoro/release/common.cfg
.kokoro/release/common.sh
.kokoro/release/drop.cfg
.kokoro/release/drop.sh
.kokoro/release/promote.cfg
.kokoro/release/promote.sh
.kokoro/release/publish_javadoc.cfg
.kokoro/release/publish_javadoc.sh
.kokoro/release/snapshot.cfg
.kokoro/release/snapshot.sh
.kokoro/release/stage.cfg
.kokoro/release/stage.sh
.kokoro/trampoline.sh
CODE_OF_CONDUCT.md
CONTRIBUTING.md
LICENSE
README.md
codecov.yaml
java.header
license-checks.xml
renovate.json
2020-03-13 14:40:53,101 synthtool > Wrote metadata to synth.metadata.

```
</details>

.github/PULL_REQUEST_TEMPLATE.md

@@ -1 +1,7 @@
-Fixes #<issue_number_goes_here> (it's a good idea to open an issue first for context and/or discussion)
+Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
+- [ ] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/java-bigquery/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
+- [ ] Ensure the tests and linter pass
+- [ ] Code coverage does not decrease (if any source code was changed)
+- [ ] Appropriate docs were updated (if necessary)
+
+Fixes #<issue_number_goes_here> ☕️

synth.metadata

@@ -1,11 +1,11 @@
 {
-  "updateTime": "2020-02-24T22:40:35.722548Z",
+  "updateTime": "2020-03-13T21:40:53.101392Z",
   "sources": [
     {
       "generator": {
         "name": "artman",
-        "version": "0.45.1",
-        "dockerImage": "googleapis/artman@sha256:36956ca6a4dc70a59de5d5d0fd35061b050bb56884516f0898f46d8220f25738"
+        "version": "1.1.0",
+        "dockerImage": "googleapis/artman@sha256:f54b7644a1d2e7a37b23f5c0dfe9bba473e41c675002a507a244389e27487ca9"
       }
     },
     {