github: update issue templates (#2178)

Summary:
This commit adds issue templates for bug reports, feature requests, and
installation problems, with specific instructions for each.

This also resolves the nag from GitHub to move to the new issue template
workflow.

I created these by following the “issue template wizard” described here:
<https://help.github.com/en/articles/creating-issue-templates-for-your-repository>

Test Plan:
I’ve committed this to the default branch of my fork. Try drafting an
issue there: <https://github.com/wchargin/tensorboard/issues/>.

wchargin-branch: github-issue-templates

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,40 @@
+---
+name: Bug report
+about: Report a problem in TensorBoard
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+Consider Stack Overflow for getting support using TensorBoard—they have
+a larger community with better searchability:
+
+https://stackoverflow.com/questions/tagged/tensorboard
+
+Do not use this template for for setup, installation, or configuration
+issues. Instead, use the “installation problem” issue template:
+
+https://github.com/tensorflow/tensorboard/issues/new?template=installation_problem.md
+
+To report a problem with TensorBoard itself, please fill out the
+remainder of this template.
+
+## Environment information (required)
+
+Please run `diagnose_tensorboard.py` (link below) in the same
+environment from which you normally run TensorFlow/TensorBoard, and
+paste the output here:
+
+https://raw.githubusercontent.com/tensorflow/tensorboard/master/tensorboard/tools/diagnose_tensorboard.py
+
+For browser-related issues, please additionally specify:
+
+  - Browser type and version (e.g., Chrome 64.0.3282.140):
+  - Screenshot, if it’s a visual issue:
+
+## Issue description
+
+Please describe the bug as clearly as possible. How can we reproduce the
+problem without additional resources (including external data files and
+proprietary Python modules)?

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,11 @@
+---
+name: Feature request
+about: Suggest an enhancement to TensorBoard
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+Please describe the problem that you’re facing and the enhancements that
+you’d like to see. Feel free to include screenshots or code samples.

.github/ISSUE_TEMPLATE/installation_problem.md

@@ -0,0 +1,31 @@
+---
+name: Installation problem
+about: Report a problem installing or starting TensorBoard
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+Use this template if you have a problem building, installing,
+configuring, or starting TensorBoard and you suspect that there is a
+problem with TensorBoard itself.
+
+Consider first reaching out to Stack Overflow for support—they have a
+larger community with better searchability:
+
+https://stackoverflow.com/questions/tagged/tensorboard
+
+## Environment information (required)
+
+Please run `diagnose_tensorboard.py` (link below) in the same
+environment from which you normally run TensorFlow/TensorBoard, and
+paste the output here:
+
+https://raw.githubusercontent.com/tensorflow/tensorboard/master/tensorboard/tools/diagnose_tensorboard.py
+
+## Steps to reproduce (required)
+
+Please provide explicit commands to reproduce the problem in a fresh
+environment (virtualenv, Conda environment, …). Include any necessary
+configuration, such as Conda `environment.yml` files.