doc: enhance GitHub template.

- add issue and PR guide.
- rewrite templates

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,45 @@
+<!--
+How to write a good issue?
+
+Read https://github.com/containous/traefik/blob/master/.github/how-to-write-a-good-issue.md
+
+And the contributing guide: https://github.com/containous/traefik/blob/master/.github/CONTRIBUTING.md
+-->
+
+### Do you want to request a *feature* or report a *bug*?
+
+
+
+### What did you do?
+
+
+
+### What did you expect to see?
+
+
+
+### What did you see instead?
+
+
+
+### Output of `traefik version`: (_What version of Traefik are you using?_)
+
+```
+(paste your output here)
+```
+
+### What is your environment & configuration (arguments, toml, provider, platform, ...)?
+
+```toml
+# (paste your configuration here)
+```
+<!--
+Add more configuration information here.
+-->
+
+
+### If applicable, please paste the log output in debug mode (`--debug` switch)
+
+```
+(paste your output here)
+```