add `point` to the glossary and link a use of it

src/appendix/glossary.md

@@ -50,6 +50,7 @@ newtype                 |  a "newtype" is a wrapper around some other type (e.g.
 NLL                     | [non-lexical lifetimes](../borrow_check/region_inference.html), an extension to Rust's borrowing system to make it be based on the control-flow graph.
 node-id or NodeId       |  an index identifying a particular node in the AST or HIR; gradually being phased out and replaced with `HirId`.
 obligation              |  something that must be proven by the trait system ([see more](../traits/resolution.html))
+point                   |  used in the NLL analysis to refer to some particular location in the MIR; typically used to refer to a node in the control-flow graph.
 projection              |  a general term for a "relative path", e.g. `x.f` is a "field projection", and `T::Item` is an ["associated type projection"](../traits/goals-and-clauses.html#trait-ref)
 promoted constants      |  constants extracted from a function and lifted to static scope; see [this section](../mir/index.html#promoted) for more details.
 provider                |  the function that executes a query ([see more](../query.html))

src/borrow_check/region_inference/constraint_propagation.md

@@ -51,10 +51,12 @@ in the section on outlives constraints.
 ## Liveness constraints
 
 A **liveness constraint** arises when some variable whose type
-includes a region R is live at some point P. This simply means that
+includes a region R is live at some [point] P. This simply means that
 the value of R must include the point P. Liveness constraints are
 computed by the MIR type checker.
 
+[point]: ../../appendix/glossary.html
+
 A liveness constraint `R live at E` is satisfied if `E` is a member of
 `Values(R)`. So to "apply" such a constraint to `Values`, we just have
 to compute `Values(R) = Values(R) union {E}`.