Auto merge of #11842 - epage:design, r=ehuss

docs(contrib): Move Design Principles earlier in the book

This is the framing by which all contributions should happen, so this should come first before getting into what is needed to know to implement a change and test it.

This is also prep for adding a new Implementations Practices section to pull out various tips spread through the Architecture section.  See #11841

Author: bors

src/doc/contrib/src/SUMMARY.md

@@ -6,6 +6,7 @@
     - [Working on Cargo](./process/working-on-cargo.md)
     - [Release process](./process/release.md)
     - [Unstable features](./process/unstable.md)
+- [Design Principles](./design.md)
 - [Architecture](./architecture/index.md)
     - [Codebase Overview](./architecture/codebase.md)
     - [SubCommands](./architecture/subcommands.md)
@@ -18,4 +19,3 @@
     - [Writing Tests](./tests/writing.md)
     - [Benchmarking and Profiling](./tests/profiling.md)
     - [Crater](./tests/crater.md)
-- [Design Principles](./design.md)