Edit and (try to) improve issue templates

The edits here are an attempt to do the following:

- Use Markdown section headings instead of `**` bold facing text
- Remove some redundant sections
- Make the descriptions and headings all follow the same style
- Try to make the text slightly more clear in a few places

This partly half of quantumlib#6972. The other half (using issue forms) can be
left for some later date.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -1,32 +1,33 @@
 ---
 name: Bug report
-about: Create a report to help us improve
+about: Report a bug or problem in Cirq or the project
 title: ''
 labels: 'kind/bug-report'
 assignees: ''
-
 ---
+## Describe the issue
 
-**Description of the issue**
 
-**How to reproduce the issue**
+## Explain how to reproduce the bug or problem
 
 ```
 
-put code in code blocks *like this*
+Put code in Markdown code blocks *like this*.
 
 ```
 
 <details>
 
-put long logs in details blocks *like this*
+Put long logs in HTML details blocks *like this*.
 
 </details>
 
-**Cirq version**
-You can get the cirq version by printing `cirq.__version__`. From the command line:
+
+## Tell us the version of Cirq where this happens
+
+You can get the Cirq version you are running by using Python
+to print the value of `cirq.__version__`. From the command line:
 
 ```
 python -c 'import cirq; print(cirq.__version__)'
 ```
-

.github/ISSUE_TEMPLATE/design_discussion.md

@@ -1,20 +1,16 @@
 ---
 name: Design discussion
-about: Start a conversation on a design problem / opportunity
+about: Start a conversation about a design problem or opportunity
 title: ''
 labels: 'kind/design-issue'
 assignees: ''
-
 ---
-
-<!-- 
-Note: this is an open ended discussion that may or may not become a feature. 
-If you are blocked by this, please raise a feature request instead. 
+<!--
+Note: this type of issue is for open-ended discussions that may
+or may not be implemented. If you are blocked by the problem,
+please open a feature request instead.
 -->
-
-**Is your design idea/issue related to a use case or problem? Please describe.**
-
-
-**Describe your design idea/issue**
+## Is your design idea/issue related to a use case or problem? Please explain
 
 
+## Describe your design idea/issue

.github/ISSUE_TEMPLATE/feature_request.md

@@ -1,30 +1,28 @@
 ---
 name: Feature request
-about: Submit a feature request 
+about: Request a new feature or change in Cirq or the project
 title: ''
 labels: 'kind/feature-request'
 assignees: ''
-
 ---
+## Is your feature request related to a use case or problem? Please explain
 
-**Is your feature request related to a use case or problem? Please describe.**
-
-
-**Describe the solution you'd like**
 
+## Describe the solution you would prefer
 
-**[optional] Describe alternatives/workarounds you've considered**
 
+## How urgent is this for you? Is it blocking important work?
 
-**[optional] Additional context (e.g. screenshots)**
+<!-- Please choose one of the following options and remove the others -->
+**P0** – this should land no later than a week
+**P1** – I need this no later than the next release
+**P2** – we should do it in the next couple of quarters
+**P3** – I'm not really blocked by it; it's an idea I'm proposing based on principle
 
 
-**What is the urgency from your perspective for this issue? Is it blocking important work?**
-<!-- Please choose one and remove the others -->
+<!-- Optional; feel free to remove the next section if it's not relevant. -->
+## Describe alternatives/workarounds you've considered
 
-P0 - this should land no later than a week
-P1 - I need this no later than the next release (end of quarter)
-P2 - we should do it in the next couple of quarters 
-P3 - I'm not really blocked by it, it is an idea I'd like to discuss / suggestion based on principle 
 
-<!-- [optional] additional comment / context -->
+<!-- Optional; feel free to remove the next section if it's not relevant. -->
+## Provide additional information or context (e.g., screenshots)

.github/ISSUE_TEMPLATE/project_health.md

@@ -1,19 +1,18 @@
 ---
-name: Project health
-about: Issues related to CI, automation infra, clean code, deprecation  
+name: Project health issue
+about: Report an issue related to CI, automation, clean code, procedures, etc.
 title: ''
 labels: 'kind/health'
 assignees: ''
-
 ---
+## Describe the issue
 
-**Description of the issue**
 
+## Tell us the version of Cirq where this happens
 
-**Cirq version**
-You can get the cirq version by printing `cirq.__version__`. From the command line:
+You can get the Cirq version you are running by using Python
+to print the value of `cirq.__version__`. From the command line:
 
 ```
 python -c 'import cirq; print(cirq.__version__)'
 ```
-

.github/ISSUE_TEMPLATE/task.md

@@ -1,19 +1,17 @@
 ---
 name: Project task
-about: Task to track larger efforts
+about: Describe a task (typically as part of a larger effort)
 title: ''
 labels: 'kind/task'
 assignees: ''
-
 ---
-
-**Summarize the task**
+## Summarize the task
 
 
-**Acceptance criteria - when is the task considered done?**
+## Acceptance criteria – when will the task be considered done?
 
 
-<!-- optional, feel free to remove this section -->
-**Related**
+<!-- Optional; feel free to remove the next section if it's not relevant. -->
+## Related issues
 
-Related issues: #abc, #xyz, ...
+Refer to related issues #abc, #xyz, ...