docs: Fix easy HTML validation errors and warnings.

"file:/srv/zulip/docs/_build/html/git/troubleshooting.html":266.5-266.12: error: Element "commit" not allowed as child of element "em" in this context. (Suppressing further errors from this subtree.)
"file:/srv/zulip/docs/_build/html/git/troubleshooting.html":266.13-266.17: error: End tag "em" violates nesting rules.
"file:/srv/zulip/docs/_build/html/overview/architecture-overview.html":211.69-211.136: error: Start tag "a" seen but an element of the same type was already open.
"file:/srv/zulip/docs/_build/html/overview/architecture-overview.html":211.171-211.174: error: Stray end tag "a".
"file:/srv/zulip/docs/_build/html/translating/hindi.html":252.36-252.48: info warning: Text run is not in Unicode Normalization Form C.
"file:/srv/zulip/docs/_build/html/tutorials/writing-views.html":469.34-469.41: error: Element "method" not allowed as child of element "p" in this context. (Suppressing further errors from this subtree.)
"file:/srv/zulip/docs/_build/html/tutorials/writing-views.html":471.122-471.125: error: End tag "p" seen, but there were open elements.
"file:/srv/zulip/docs/_build/html/tutorials/writing-views.html":469.34-469.41: error: Unclosed element "method".

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

docs/translating/hindi.md

@@ -54,7 +54,7 @@ Zulip friendly and usable.
 * Deactivate/Reactivate - **निष्क्रिय करें / पुन: सक्रिय करें**
 * Search - **खोज करें/ढूंढे**
 * Pin - **ठीक करना**
-* Mention/@mention - **ज़िक्र करना / @ ज़िक्र करना**
+* Mention/@mention - **ज़िक्र करना / @ ज़िक्र करना**
 * Invalid - **अमान्य**
 * Customization - **अनुकूलन**
 * I want - **मुझे चाहिए**