Fixes #924 Add context to dated information

Author: igaray

src/SUMMARY.md

@@ -107,7 +107,6 @@
         - [Lowering to logic](./traits/lowering-to-logic.md)
         - [Goals and clauses](./traits/goals-and-clauses.md)
         - [Canonical queries](./traits/canonical-queries.md)
-        - [Lowering module in rustc](./traits/lowering-module.md)
 - [Type checking](./type-checking.md)
     - [Method Lookup](./method-lookup.md)
     - [Variance](./variance.md)

src/about-this-guide.md

@@ -35,6 +35,21 @@ be found at the [GitHub repository]. If you find any mistakes in the
 guide, please file an issue about it, or even better, open a PR
 with a correction!
 
+### Constant change
+
+Keep in mind that `rustc` is a real production-quality product, being worked upon continuously by a sizeable set of contributors.
+As such, it has its fair share of codebase churn and technical debt.
+In addition, many of the ideas discussed throughout this guide are idealized designs that are not fully realized yet.
+
+And things keep changing so that it is
+
+making hard to keep this guide completely up to date on everything!
+
+Contributing to this guide:
+
+> “‘All conditioned things are impermanent’ — when one sees this with wisdom, one turns away from suffering.” _The Dhammapada, verse 277_
+
+
 ## Other places to find information
 
 You might also find the following sites useful:

src/overview.md

@@ -159,17 +159,6 @@ satisfy/optimize for. For example,
 So, as you read through the rest of the guide, keep these things in mind. They
 will often inform decisions that we make.
 
-### Constant change
-
-Keep in mind that `rustc` is a real production-quality product.
-As such, it has its fair share of codebase churn and technical debt. A lot of
-the designs discussed throughout this guide are idealized designs that are not
-fully realized yet. And things keep changing so that it is hard to keep this
-guide completely up to date on everything!
-
-The compiler definitely has rough edges, but because of its design it is able
-to keep up with the requirements above.
-
 ### Intermediate representations
 
 As with most compilers, `rustc` uses some intermediate representations (IRs) to

src/parallel-rustc.md

@@ -1,9 +1,10 @@
 # Parallel Compilation
 
 Most of the compiler is not parallel. This represents an opportunity for
-improving compiler performance. Much effort has been put into parallelizing
-`rustc`, but it is still pretty early days for this work. There is a lot of
-design and correctness work that needs to be done.
+improving compiler performance.
+
+As of December 2020, work on explicitly parallelizing the compiler has stalled.
+There is a lot of design and correctness work that needs to be done.
 
 One can try out the current parallel compiler work by enabling it in the
 `config.toml`.

src/the-parser.md

@@ -1,7 +1,7 @@
 # Lexing and Parsing
 
-> The parser and lexer are currently undergoing a lot of refactoring, so parts
-> of this chapter may be out of date.
+As of January 2021, the lexer and parser are undergoing refactoring to allow
+extracting them into libraries.
 
 The very first thing the compiler does is take the program (in Unicode
 characters) and turn it into something the compiler can work with more