[infer][PR] Fix minor bugs in docs

Summary:
Hi,

I have found a couple of small issues while reading the docs. The pull request contains the fixes.

BTW, the link to PLDI slices is also broken here: https://fbinfer.com/docs/absint-framework. I haven't found the slides anywhere, so not sure how to fix it.
Pull Request resolved: https://github.com/facebook/infer/pull/1278

Reviewed By: dulmarod

Differential Revision: D22018947

Pulled By: jvillard

fbshipit-source-id: 13f6d27b1

website/docs/02-separation-logic-and-biabduction.md

@@ -72,7 +72,7 @@ Now, suppose we have two resources <Math code="\\( r\_1 \\)" /> and
 <Math code="\\( r\_2 \\)" />, described by
 <Math code="\\(r\_1 \mapsto open * r\_2 \mapsto open\\)" /> and we close the
 first of them. We think operationally in terms of updating the memory in place,
-leaving \\(r_2 \mapsto open\\) alone, as described by this triple:
+leaving <Math code="\\(r\_2 \mapsto open\\)" /> alone, as described by this triple:
 
 ---
 

website/docs/04-absint-framework.md

@@ -24,7 +24,7 @@ from @Scale2016.
 
 **If you feel like coding instead of reading, a great way to get started with
 Infer.AI is to go through the lab exercise
-[here](https://github.com/facebook/infer/blob/master/infer/src/labs/lab.md).**
+[here](https://github.com/facebook/infer/blob/master/infer/src/labs/README.md).**
 
 ## By example: intraprocedural analysis