Add links and fix nits for extensions

Author: szarnyasg

README.md

@@ -59,18 +59,21 @@ pak::pak()
 ### Developing with Extensions
 
 If you wish to build or add extensions to the R package you first need to build duckdb with the `extension_static_build` flag.
-The following commands allow you to add the httpfs extension to a duckdb R build.
+The following commands allow you to add the [`httpfs` extension](https://duckdb.org/docs/extensions/httpfs) to a DuckDB R build.
 See the [extension ReadMe](https://github.com/duckdb/duckdb/tree/master/extension#readme) for more information about extensions
 
 ``` sh
 cd duckdb/
 EXTENSION_STATIC_BUILD=1 make
 ```
 
-Then in R
+Then in R, run:
 
 ``` r
 library(duckdb)
 con <- DBI::dbConnect(duckdb(config=list('allow_unsigned_extensions'='true')))
 dbExecute(con, "LOAD '{{path_to_duckdb}}/build/release/extension/httpfs/httpfs.duckdb_extension'")
 ```
+
+For more information about using extensions, see the [documentation on extensions](https://duckdb.org/docs/extensions/overview).
+For instructions on building them, see [extension README](https://github.com/duckdb/duckdb/tree/main/extension#readme).

RELEASE.md

@@ -18,7 +18,7 @@ revdepcheck::revdep_check(num_workers = 8, env=c(`MAKEVARS`="-j8"))
 ## Source Package
 The R package does not automatically pick up the DuckDB version from the git tag. Make sure the file `DESCRIPTION` in the master branch has the `Version` entry that *you want to create*.
 
-It's important that package builds are created from the main branch of the duckdb/duckdb repo (not of a fork) because otherwise the git revision ids used to install extensions are wrong.
+It's important that package builds are created from the `main` branch of the [duckdb/duckdb repository](https://github.com/duckdb/duckdb) (not of a fork) because otherwise the git revision ids used to install extensions are wrong.
 
 You can get the R source tarball either from the build artifacts (r-package-source) or from a GitHub release after CI finishes (`duckdb_[version].tar.gz`).