Remove CI status badge from README (#2187)

## Motivation
"CI status" for the develop branch is not really well-defined since we don't actually run any CI tasks on the develop branch. Bors runs them on staging, then merges to develop. If we set the status badge to develop, as it is now, it shows "no status." If we set it to staging, it'll show the status of the last bors run, which may have failed (and not been merged), which is misleading.

@noamnelke you were right, I concede :)

README.md

@@ -16,7 +16,7 @@
 [![Go Report Card](https://goreportcard.com/badge/github.com/spacemeshos/go-spacemesh)](https://goreportcard.com/report/github.com/spacemeshos/go-spacemesh)
 [![Bors enabled](https://bors.tech/images/badge_small.svg)](https://app.bors.tech/repositories/22421)
 <a href="https://godoc.org/github.com/spacemeshos/go-spacemesh"><img src="https://img.shields.io/badge/godoc-LGTM-blue.svg"/></a>
-[![CI](https://github.com/spacemeshos/go-spacemesh/workflows/CI/badge.svg?branch=develop)](https://github.com/spacemeshos/go-spacemesh/actions)
+[![CI: passing](https://img.shields.io/badge/CI-passing-success?logo=github&style=flat)](https://github.com/spacemeshos/go-spacemesh/blob/develop/ci.md#ci-status)
 </p>
 <p align="center">
 <a href="https://gitcoin.co/profile/spacemeshos" title="Push Open Source Forward">

ci.md

@@ -36,6 +36,12 @@ Note that bors also has a "dry run" mode (trigged by the command `bors try`). Th
 
 It's not necessary to run any additional tests when bors merges code to `develop`. The only thing that needs to happen on a push to `develop` is that a new docker image must be generated and pushed to dockerhub.
 
+### CI status
+
+a.k.a.: You're lying! Your "CI: passing" badge is static and doesn't reflect the true status!
+
+As described above, bors ensures that no commit to `develop` can break the build. This is why our status is always passing: it's static, but it's not a lie!
+
 ## Testing locally
 
 There is a robust tool called [`act`](https://github.com/nektos/act) that mimics the GA environment locally. It can be installed using Homebrew by running: