Add README.md

README.md

+# ``GitLab::API``
+
+Lightweight implementation of ``GitLab``'s API in Perl.
+
+## Quick start
+
+```{.pl}
+use GitLab;
+
+my $gitlab = GitLab::API->new(
+    URL        => "https://gitlab.fi.muni.cz/api/v3",
+    AuthToken  => "...",
+    DieOnError => 1
+);
+
+my $users  = $gitlab->users();
+my $groups = $gitlab->groups(search => "pb161");
+```
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