Author: Urs Format: MarkdownItexadded some references, formatting and cross-links. Also touched the wording.
<a href="https://ncatlab.org/nlab/revision/diff/Ehresmann%27s+theorem/4">diff</a>, <a href="https://ncatlab.org/nlab/revision/Ehresmann%27s+theorem/4">v4</a>, <a href="https://ncatlab.org/nlab/show/Ehresmann%27s+theorem">current</a>
added some references, formatting and cross-links. Also touched the wording.