Add names and email addresses to MAINTAINERS.md (#8473)

* Add names and email addresses to MAINTAINERS.md

This is so people can more easily reach the right people (e.g. for security
reports), and because we do it like this in other repos.

I did add parentheses to the formatting (different than in other
MAINTAINERS.md) to make it more readable, this this repo is more complex.

Signed-off-by: Julius Volz <julius.volz@gmail.com>

* Update Björn's email address

Signed-off-by: Julius Volz <julius.volz@gmail.com>

MAINTAINERS.md

@@ -1,17 +1,17 @@
-@roidelapluie is the main/default maintainer, some parts of the codebase have other maintainers:
+Julien Pivotto (<roidelapluie@prometheus.io> / @roidelapluie) is the main/default maintainer, some parts of the codebase have other maintainers:
 
 * `cmd`
-  * `promtool`: @simonpasquier
+  * `promtool`: Simon Pasquier (<pasquier.simon@gmail.com> / @simonpasquier)
 * `discovery`
-  * `k8s`: @brancz
+  * `k8s`: Frederic Branczyk (<fbranczyk@gmail.com> / @brancz)
 * `documentation`
-  * `prometheus-mixin`: @beorn7
+  * `prometheus-mixin`: Björn Rabenstein (<beorn@grafana.com> / @beorn7)
 * `storage`
-  * `remote`: @csmarchbanks, @cstyan, @bwplotka
-* `tsdb`: @codesome, @bwplotka
+  * `remote`: Chris Marchbanks (<csmarchbanks@gmail.com> / @csmarchbanks), Callum Styan (<callumstyan@gmail.com> / @cstyan), Bartłomiej Płotka (<bwplotka@gmail.com> / @bwplotka)
+* `tsdb`: Ganesh Vernekar (<ganesh@grafana.com> / @codesome), Bartłomiej Płotka (<bwplotka@gmail.com> / @bwplotka)
 * `web`
-  * `ui`: @juliusv
-* `Makefile` and related build configuration: @simonpasquier, @SuperQ
+  * `ui`: Julius Volz (<julius.volz@gmail.com> / @juliusv)
+* `Makefile` and related build configuration: Simon Pasquier (<pasquier.simon@gmail.com> / @simonpasquier), Ben Kochie (<superq@gmail.com> / @SuperQ)
 
 For the sake of brevity, not all subtrees are explicitly listed. Due to the
 size of this repository, the natural changes in focus of maintainers over time,