readme: List subversion as dependency

docker: Install subversion in docker container

Signed-off-by: Dennisbonke <admin@dennisbonke.com>

README.md

@@ -62,7 +62,7 @@ Now proceed to the Building paragraph.
 
 1.  Certain programs are required to build managarm;
     here we list the corresponding Debian packages:
-    `build-essential`, `pkg-config`, `autopoint`, `bison`, `curl`, `flex`, `gettext`, `git`, `gperf`, `help2man`, `m4`, `mercurial`, `ninja-build`, `python3-mako`, `python3-protobuf`, `python3-yaml`, `texinfo`, `unzip`, `wget`, `xsltproc`, `xz-utils`, `libexpat1-dev`, `rsync`, `python3-pip`, `python3-libxml2`, `netpbm`, `itstool`, `zlib1g-dev`, `libgmp-dev`, `libmpfr-dev`, `libmpc-dev`.
+    `build-essential`, `pkg-config`, `autopoint`, `bison`, `curl`, `flex`, `gettext`, `git`, `gperf`, `help2man`, `m4`, `mercurial`, `ninja-build`, `python3-mako`, `python3-protobuf`, `python3-yaml`, `texinfo`, `unzip`, `wget`, `xsltproc`, `xz-utils`, `libexpat1-dev`, `rsync`, `python3-pip`, `python3-libxml2`, `netpbm`, `itstool`, `zlib1g-dev`, `libgmp-dev`, `libmpfr-dev`, `libmpc-dev`, `subversion`.
 1.  `meson` is required. There is a Debian package, but as of Debian Stretch, a newer version is required.
     Install it from pip: `pip3 install meson`.
 1.  The [xbstrap](https://github.com/managarm/xbstrap) tool is required to build managarm. Install it from pip: `pip3 install xbstrap`.

docker/Dockerfile

@@ -31,6 +31,7 @@ RUN apt-get update \
 		python3-protobuf \
 		python3-yaml \
 		rsync \
+		subversion \
 		texinfo \
 		unzip \
 		wget \