Fix hidden title in rustdoc book

[ickk]

raw html is treated as actual html by markdown, so this title needs to use some form of escaping in order to display correctly

[rustbot]

r? @notriddle

rustbot has assigned @notriddle.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[notriddle]

@bors r+

[bors]

📌 Commit 4850615 has been approved by notriddle

It is now in the queue for this repository.

[bors]

⌛ Testing commit 4850615 with merge d25cf6f...

[bors]

☀️ Test successful - checks-actions
Approved by: notriddle
Pushing d25cf6f to master...

[rust-timer]

Finished benchmarking commit (d25cf6f): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.4%, 2.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-2.0%, 2.4%]	2

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.2%	[1.2%, 1.2%]	1
Improvements ✅ (primary)	-1.0%	[-1.0%, -1.0%]	1
Improvements ✅ (secondary)	-4.5%	[-6.6%, -2.5%]	2
All ❌✅ (primary)	-1.0%	[-1.0%, -1.0%]	1

Binary size

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-0.2%, -0.2%]	1

Bootstrap: 675.939s -> 676.904s (0.14%)
Artifact size: 315.95 MiB -> 316.08 MiB (0.04%)