Fix Makefiles and add README

The http/ and hashtable/ Makefiles named sources that do not exist
(test.c, net.c, net.h in http/; http.h in hashtable/) and had no way to
find the sibling hashtable/llist sources they link against, so neither
directory built at all. Both now compile those sources with explicit
recipes.

VPATH would be the terser fix but is deliberately avoided: it searches
for targets as well as sources, so a stale ../llist/test.o gets linked
in place of a freshly compiled one, and hashtable/test silently runs the
linked-list suite instead of its own.

llist/Makefile built fine; its .PHONY read "all," with a comma, making
that the literal target name, and test.o was missing its llist.h
dependency.

README covers layout, build, run, the use()/Handler routing API, and the
library tests.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -1 +1,71 @@
-Addon Libraries to C Programming Language
+# pico-http
+
+A minimal HTTP server in C, with the hashtable and linked-list libraries it is built on.
+
+## Layout
+
+```
+http/       server and routing framework
+hashtable/  route table
+llist/      bucket chaining for the hashtable
+```
+
+## Build
+
+Needs `gcc` and `make`.
+
+```sh
+cd http && make
+```
+
+## Run
+
+```sh
+./pico-http
+```
+
+Listens on port 3000, set by `PORT` in `http/http.h`.
+
+```sh
+$ curl localhost:3000/login
+Login works!
+
+$ curl localhost:3000/signup
+Sign Up works!
+```
+
+Unregistered paths return `400 Bad request`.
+
+## Adding a route
+
+A handler fills in `Res`:
+
+```c
+void hello(Req* req, Res* res)
+{
+    char* content = "Hello\n";
+
+    res->status = 200;
+    res->content_type = "text/html";
+    res->content_length = strlen(content);
+    res->body = content;
+}
+```
+
+Register it before starting the server, in `main.c`:
+
+```c
+use("/hello", &hello);
+http_start(PORT);
+```
+
+Paths match exactly — `/hello` will not match `/hello/`.
+
+## Library tests
+
+```sh
+cd llist && make && ./test
+cd hashtable && make && ./test
+```
+
+`make clean` in any of the three directories removes its objects and binary.