Improve build instructions (#108)

.gitignore

@@ -5,3 +5,4 @@
 
 _build/**
 venv
+docs/_build/

README.md

@@ -4,17 +4,40 @@ This contains the source for QuPath's documentation, hosted at https://qupath.re
 
 ## Building locally
 
-To build this locally, you should first install (possibly in a [venv](https://docs.python.org/3/library/venv.html)):
-- `sphinx-build`
-- `sphinx_rtd_theme`
-- `myst_parser`
-- `readthedocs-sphinx-search`
+To build this locally, create a virtual environment, eg:
 
-As well as the command line tool `Make` (e.g., [GNU Make](https://www.gnu.org/software/make/)).
+```bash
+python -m venv ./venv
+. ./venv/bin/activate
+```
+
+or using conda/mamba:
+
+```bash
+conda env create -n qupath-docs python=3.12
+conda activate qupath-docs
+```
+
+Then install the requirements for this repo:
+
+```bash
+pip install -r requirements.txt
+```
+
+You'll also need the command line tool `Make` (e.g., [GNU Make](https://www.gnu.org/software/make/)).
 
 Then, you can run `make` to see available build options.
 `make html` will make the HTML version of the website, which is probably the
-most useful option.
+most useful option. The built HTML files will be in `_build/html`, and can
+be opened in a web browser without running a local HTTP server.
+
+Alternatively, you can install `sphinx-autobuild` and `watchfiles`
+into your virtual environment to run a HTTP server and have the HTML files
+automatically rebuilt when any changes are made:
+
+```bash
+sphinx-autobuild . _build/html
+```
 
 ## License